Genome-wide Association Analysis of Fast Chlorophyll Fluorescence Parameters in Maize

Fast chlorophyll fluorescence parameters are widely used to characterize the photosynthetic efficiency of plants. In this study, a genome-wide association analysis was used to detect key single-nueleotide polymorphisms （SNPs） associated with fast chlorophyll fluorescence parameters using more than 560 000 SNPs in a maize panel consisting of 404 inbred lines. In four fidd environments, 41 SNPs were detected to be associated with five fast chlorophyll fluorescence parameters, including ABS/CS0, ET0/CS0, TR0/ABS, ET0/TR0 and Pies. Among these identified SNPs, 8, 6, 18, 4 and 5 were significantly associated with ET0/TR0, ABS/ CS0, TR0/ABS, ET0/CS, and Plcs, respectively. These SNPs will help to discover genes for chlorophyll fluorescence parameters, better understand the genetic basis of photosynthesis, and assist in developing marker-assisted selection breeding programs in maize.

Evaluation of Chlorophyll Content and Fluorescence Parameters as Indicators of Drought Tolerance in Barley

Drought is a major abiotic stress that severely affects food production worldwide. Agronomic and physiological traits associated with drought tolerance are suitable indicators for selection of drought tolerance genotypes to reduce the impact of water deficit on crop yield in breeding program. The objective of this study was to identify indicators related to drought tolerance through analysis of photosynthetic traits in barley （Hordeum vulgare L.）. These traits included chlorophyll content, initial fluorescence （Fo）, maximum primary yield of photochemistry of photosystem Ⅱ （Fv /Fo） and maximum quantum yield of photosystem Ⅱ （Fv/Fm）. Four genotypes （Tadmor, Arta, Morocco9-75 and WI2291） variable in drought tolerance were used to investigate the correlation between these traits and drought tolerance. The results reflected that all of these traits were affected negatively in the four genotypes at different levels of post-anthesis drought stress, but the decrease in drought tolerant genotypes was much less than that of drought sensitive genotypes. The results further revealed that the components of the photosynthetic apparatus could be damaged significantly in drought sensitive genotypes, while drought tolerant genotypes were relatively less affected. On the other hand, the values of chlorophyll content, Fo, Fv/Fo and Fv/Fm in drought tolerance genotypes were significantly higher than those in drought sensitive genotypes under drought stress. It was concluded that chlorophyll content, Fo, Fv/Fo and Fv/Fm could be considered as reliable indicators in screening barley germplasm for drought tolerance.

Quantitative genetic analysis of chlorophyll a fluorescence parameters in maize in the field environments

Chlorophyl fluorescence transient from initial to maximum fluorescence （“P”step） throughout two intermedi-ate steps （“J”and“I”） （JIP-test） is considered a reliable early quantitative indicator of stress in plants. The JIP-test is particularly useful for crop plants when applied in variable field environments. The aim of the present study was to conduct a quantitative trait loci （QTL） analysis for nine JIP-test parameters in maize during flowering in four field environ-ments differing in weather conditions. QTL analysis and identification of putative candidate genes might help to explain the genetic relationship between photosynthesis and different field scenarios in maize plants. The JIP-test param-eters were analyzed in the intermated B73 ？ Mo17 （IBM） maize population of 205 recombinant inbred lines. A set of 2,178 molecular markers across the whole maize genome was used for QTL analysis revealing 10 significant QTLs for seven JIP-test parameters, of which five were co-localized when combined＆amp;nbsp;over the four environments indicating polygenic inheritance and pleiotropy. Our results demonstrate that QTL analysis of chlorophyl fluorescence parameters was capable of detecting one pleiotropic locus on chromosome 7, coinciding with the gene gst23 that may be associated with efficient photosynthe-sis under different field scenarios.

Effects of drought stress on photosynthesis and chlorophyll fluorescence images of soybean(Glycine max)seedlings

The main purpose of this research is to provide a theoretical foundation for the screening of drought-resistant soybean varieties and to establish an efficient method to detect the PSII actual photochemical quantum yields efficiently.Three soybean varieties were compared in this experiment after 15 d when they were planted in a greenhouse.These varieties were then exposed to light drought stress(LD)and serious drought stress(SD)conditions.With five times’measurement,chlorophyll fluorescence and soil-plant analysis development considered as the main basis for this study.Several parameters in SD conditions significantly reduced,such as net photosynthetic rates(Pn),stomatal conductance(Gs),PSII primary light energy conversion efficiency(Fv/FM),PSII actual photochemical quantum yields[Y(II)],photochemical quenching coefficient(qP)and non-photochemical quenching coefficient(qN).The soybeans in the seedling stage adapted to the inhibitory effect of drought stress on photosynthesis through stomatal limitation.Under serious drought stress,non-stomatal limitation damaged the plant photosynthetic system.The amplitudes of Pn and Y(II)of drought-resistant Qihuang 35 were lower than those of the two other varieties.Based on the data of this study,a new method had been developed to detect Y(II)which reflected the photosynthetic capacity of plant,R=0.85989,u=0.048803 when using multiple linear regression,and R=0.84285,u=0.054739 when using partial least square regression.

Influence of water potential and soil type on conventional japonica super rice yield and soil enzyme activities

We carried out a pool culture experiment to determine the optimal water treatment depth in loam and clay soils during the late growth stage of super rice. Three controlled water depth treatments of 0-5, 0-10 and 0-15 cm below the soil surface were established using alternate wetting and drying irrigation, and the soil water potential （0 to -25 kPa） was measured at 5, 10 and 15 cm. A 2-cm water layer was used as the control. We measured soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and rice yield. The results showed that the 0-5-cm water depth treatment significantly increased root antioxidant enzyme activities in loam soil compared with the control, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield did not differ from those of the control. The 0-10- and 0-15-cm water depth treatments also increased root antioxidant enzyme activities, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield decreased. In clay soil, the soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and yield did not change with the 0-5-cm water treatment, whereas the 0-10- and 0-15-cm water treatments improved these parameters. Therefore,the appropriate depths for soil water during the late growth period of rice with a 0 to -25 kPa water potential were 5 cm in loam and 15 cm in clay soil.

Physiological Mechanisms of Delaying Leaf Senescence in Maize Treated with Compound Mixtures of DCPTA and CCC

At the beginning of silking, maize production began to form, but leaves started senescence and photosynthetic capacity decreased at this time, all of those severely restricted the formation of the production. In order to study the effects of exogenous substances on the process of leaf senescence, 40 mg. L-1 DCPTA and 20 mg. L-1 CCC were mixed in the research. When the maize grew to the six expanded leaves stage, 10 mL compound mixtures （TR） were sprayed on both sides of leaves for per plant, and the control was treated with water （CK）. Three plants were selected randomly for determination of physiological index at 10, 20, 30, 40 and 50 days after silking. The results showed that TR could increase the chlorophyll content significantly, FvFm, Fv/F0 and Y（Ⅱ） values of TR were higher than those of CK while F0 values were opposite. Compared with CK, TR increased SOD and POD activities and soluble protein content, and reduced MDA content. Correlation analysis showed that chlorophyll content had negative correlation with F0, and MDA content had negative correlation with other indexes. Compared with CK, TR reduced the negative correlation effect between chlorophyll content and MDA, increased the positive correlation effect between chlorophyll content and Fv/Fm, SOD, PODI and soluble protein. The study provided theoretical and experimental evidence for the application of the compound mixtures of DCPTA and CCC to the production.

Wheat growth, photosynthesis and physiological characteristics under different soil Zn levels

In recent years,heavy metal hazards in the soil have seriously affected agricultural production.This study aims to examine the effects of different levels of heavy metal Zn on the growth,photosynthesis and physiological characteristics of wheat,and provide a theoretical basis for the diagnosis and control of heavy metal pollution in agricultural production.The field test method was used to explore the changes of wheat agronomic traits,photosynthetic capacity,chlorophyll fluorescence parameters,spectral characteristic curve,active oxygen metabolism system,cell ultrastructure,and yield,under different Zn levels(0,250,500,750,and 1000 mg kg^(-1)).The results show that,low-level Zn treatments can effectively promote the synthesis of wheat chlorophyll,improve photosynthetic capacity,and increase yield.The yield of ZnL1(250 mg kg^(-1))was the highest in the two-year test,which increased by 20.4%in 2018 and 13.9%in 2019 compared with CK(0 mg kg^(-1)).However,a high Zn level had a significant stress effect on the photosystem of wheat.PIabs(reaction center performance index)and Fv/Fm(maximum photochemical efficiency)were significantly reduced,the active oxygen metabolism system was damaged,and the photosynthetic capacity was reduced,which in turn led to reduced yield.Among them,the yield of ZnL4(1000 mg kg^(-1))was the lowest in the two-year test,which was 28.1 and 16.4%lower than CK in 2018 and 2019,respectively.The green peak position of ZnL3 and ZnL4 had"red shift"to the long wave direction,while the red valley position of ZnL4 had"blue shift"to the short wave direction.Under ZnL4,some wheat leaf organelles began to decompose,vacuoles increased,cytoplasm decreased,cell walls thickened,chloroplast basal lamellae were disordered,and mitochondrial membranes disintegrated.Stepwise regression and Path analysis showed that Pn(net photosynthetic rate)played a leading role in the formation of yield.Redundancy(RDA)analysis showed that the optimal Zn level for wheat growth was about 250 mg kg^(-1),and wheat would be stressed when the soil Zn level exceeded 500 mg kg^(-1) in the test condition of this study.Findings of this study provide a theoretical basis for the diagnosis and prevention of heavy metal(Zn)pollution in the soil.

Changes in photosynthesis and chlorophyll fluorescence in two soybean (Glycine max) varieties under NaCl stress

Traditional detection methods of crop information are often destructive and low efficiency.In this study,a new evaluation method was developed based on photosynthesis and chlorophyll fluorescence.Via analysis of the changes under NaCl stress during the seedling stage of two varieties,the salt resistance mechanism of soybeans was explored and a non-destructive stress-recognition method was developed.In this experiment,two soybean varieties were treated with one of four levels of NaCl stress:CK(0 mmol/L),LS(50 mmol/L),MS(100 mmol/L),and HS(150 mmol/L),for 15 d.The normal functions of the photosynthetic system of soybeans were enhanced under LS NaCl stress,but were inhibited under HS NaCl stress.Biomass,net leaf photosynthetic rate(Pn),stomatal conductance(gs),intercellular carbon dioxide concentration(Ci),transpiration rate(Tr),chlorophyll fluorescence parameters Y(II)and PSII decreased.However,in contrast to the findings of other studies on the influence of severe drought stress on soybean for long periods in which non-photochemical quenching coefficient(qN)decreased,this parameter increased under salt stress in soybean.The results demonstrate that the method developed is a promising tool for rapid and non-destructive detection of soybean photosynthetic responses under salt stress in the field.

Effects of Drought Stress on Key Enzymes of Carbon Metabolism, Photosynthetic Characteristics and Agronomic Traits of Soybean at the Flowering Stage under Different Soil Substrates

Soybean is an important legume food crop,and its seeds are rich in nutrients,providing humans and animals with edible oil and protein feed.However,soybean is sensitive to water requirements,and drought is an important factor limiting soybean yield and quality.This study used Heinong 84(drought resistant variety)and Hefeng 46(intermediate variety)as tested varieties planted in chernozem,albic,and black soils.The effects of drought stress on the activities of key enzymes in carbon metabolism and photosynthetic characteristics of soybean were studied during the flowering stage,most sensitive to water.(1)The activities of SS-1,6PGDH,and G6PDH enzymes in soybean leaves first increased and then decreased under drought stress.The enzyme activity was the highest under moderate drought stress and weakest in the blank group.(2)Drought stress increased Phi2,PhiNO,and Fm in soybean leaves and reached the highest value under severe drought;with the increase in drought stress,PhiNPQ and Fv/Fm of soybean leaves gradually decreased,reaching the lowest under severe drought.(3)With the increase in drought stress,F0 and Fs of soybean leaves showed a single peak curve,and the maximum was at moderate drought.(4)Correlation analysis showed that F0 was greatly affected by varieties and soil types;Fs,F0,and Fm soil varieties had a great influence,and chlorophyll fluorescence parameters were affected differently under drought stress with different drought degrees.(5)Drought stress changed the agronomic traits and yield of soybean.With the increase of drought degree,plant height,node number of main stem,effective pod number,100-seed weight and total yield decreased continuously.(6)Drought stress affected the dry matter accumulation of soybean.With the increase of drought degree,the dry matter accumulation gradually decreased.Among them,the leaf was most seriously affected by drought,and SD decreased by about 55%compared with CK.Under the condition of black soil,the dry matter accumulation of soybean was least affected by drought.

Effects of Temperature and Light on Growth Rate and Photosynthetic Characteristics of Sargassum horneri

The changing environmental factors exerted great influences on coastal macroalgal communities.To study the responses of the brown seaweed Sargassum horneri to temperature and light,S.horneri was cultured under three temperatures(20,25 and 30℃)and three light intensities(30,60,and 120μmol photons m-2 s-1)for seven days.The growth rate,chlorophyll a(Chl a)and carotenoids(Car)contents,chlorophyll fluorescence,and photosynthetic oxygen evolution rate were measured.The results show that the highest relative growth rate(RGR),maximal electron transport rate(rETRmax);the net photosynthetic rate(Pn)were observed at the lowest temperature(20℃)and highest light intensity(120μmol photons m-2 s-1);and the RGR and Pn were significantly inhibited by the highest temperature(30℃),especially at the lowest light intensity(30μmol photons m-2 s-1)(P<0.05).Additionally,the highest light intensity enhanced the non-photochemical quenching(NPQ)even under the highest temperature(30℃),indicating that the higher light intensity could induce photo-protection reaction of thalli.These results suggest that the higher temperature and lower light intensity exerted negative influences on S.horneri.

Effects of Rooting Agents on Growth and Photosynthetic Traits of Sudan Grasses

[Objective] To investigate the effects of rooting agents on the growth and photosynthetic traits of Sudan grasses. [ Method] The responses of the growth and some photosynthetic traits of Sudan grasses to three NK II rooting agents were determined according to the randomized complete block design. [ Result] Compared to control treatment, the Sudan grass treated by NK 11-298 showed higher chlorophyll a and carotenoid contents, higher chlorophyll fluorescence parameter values （ PSII quantum efficiency： ФPSII; photochemical quenching： qP; and electron transport rate： ETR）, higher maximum photosynthetic rate （Pmax） and respiration rate （ Rd）, and the highest biomass accumulation. The chlorophyU fluorescence parameter values of Sudan grasses treated by NK 11-888 and NK 11-16 were higher than those of control treatment （ P 〈 0.05）, and other indexes had no significant difference. [ Conclusion] The rooting agents should be selected carefully according to their practice aims because of sensibility of Sudan grass to rooting agents.

Hormesis-like growth and photosynthetic physiology of marine diatom Phaeodactylum tricornutum Bohlin exposed to polystyrene microplastics

The effects of pristine polystyrene microplastics(pMPs)without any pretreatment at different concentrations(0,10,20,50,and 100 mg/L)on Phaeodactylum tricornutum Bohlin at two initial algae densities(105 and 106 cells/mL)were assessed in this study.Hormesis-like effects were found when microalgae grew with pMPs.The results showed that pMPs inhibited microalgae growth under a high concentration of microplastics tolerated by individual algal cell(low initial algae density)(up to-80.189.71%)but promoted growth when the situation was opposite(up to 15.273.66%).The contents of photosynthetic pigments including chlorophyll a,chlorophyll c and carotenoids showed resistance to pMPs stress under a low initial algae density and increased with time,but the opposite was true under a high initial algae density.Compared with the low initial algae density group,Qp received less inhibition,and NPQ(heat dissipation)also decreased under the high initial algae density.Under the low initial algae density,OJIP parameters such as Sm,N,Area,Pi Abs,ѱo,φEo,TRo/RC and ETo/RC were more perturbed initially and returned to the levels of the control group(without pMPs)over time,but they remained stable throughout the experiment at high initial algae density.These results show that microplastics in the marine environment may have different toxic effects on P.tricornutum at different growth stages,which is of great significance for understanding the impact of microplastics on marine microalgae and aquatic ecosystems.