Systemic Activation of Defensive Enzymes and Protection in Tobacco Plantlets against <i>Phytophthora nicotianae</i>Induced by Oligosaccharins

Oligosaccharins are potent biomolecules which activate defense responses and resistance in tobacco plants. However, it is not known the systemic behavior of defensive enzymes activated by these elicitors. In this work, the dynamic behavior of key defensive enzymes was evaluated in tobacco plant leaves previously treated through the roots with chitosan polymer (CH), chitosan (COS) and pectic (OGAS) oligosaccharides and Spermine (Sp). All macromolecules tested activated protein levels and defense enzymatic activity in tobacco leaves but with different response dynamics among them and depending on the biochemical variable evaluated. Defense response above control levels were detected since 12 hours after treatments and it consisted in a biphasic behavior with two peaks for PAL (EC 4.3.1.5) and β 1 - 3 glucanase (EC 3.2.1.6) enzymatic activities. The highest enzymatic levels for these enzymes were achieved at 48 hours in plantlets elicited with COS and at 72 hours for those plants treated with chitosan polymer, while the highest POD (EC 1.11.1.6) activity was detected with CH between 48 and 72 hours. These results demonstrated systemic defense activation by oligosaccharins in tobacco whose dynamic of defense response is affected by the kind of oligosaccharins tested. When applying OGAS by foliar spray on tobacco, systemic resistance against Phytoththora nicotianae was induced and plantlets were protected with the low concentration tested by 46% under the bioassays conditions performed. Moreover, enzymatic determinations on roots and leaves previous to plant-pathogen interaction showed increments above 30% of control levels for PAL and POD activities. It means that oligosaccharins activate local and systemic defense responses in plants in the absent of pathogen infection.

Influences of ascorbic acid and gibberellic acid in alleviating effects of salinity in Petunia under in vitro

Salinity is one of the abiotic stresses that limits the growth and productivity of many crops.A possible survival strategy for plant under saline conditions is to use compounds that could minimize the harmful effects of salt stress on the plant development.The objective of the presented study was to investigate the effect of exogenous ascorbic acid(ASA)with or without gibberellic acid(GA3)on key growth and biochemical parameters in two petunia cultivars‘Prism Rose’and‘Prism White’under saline(150 mM NaCl)and non-saline in vitro condition.Nodal cutting with an axillary buds were used as explants.Application of 1 mM ascorbic acid with or without 0.05 mM gibberellic acid into the MS medium stimulated the length of shoots and the number of new shoots of‘Prism Rose’;whereas,it decreased the root length and the number of roots of both‘Prism Rose’and‘Prism White’under non-saline condition.The addition of ascorbic acid with or without gibberellic acid into the MS medium under saline condition,increased the length of plants and the number of new shoots,but did not affect their root number and length.NaCl treatments increased the proline content and lipid peroxidation which was indicated by the accumulation of malondialdehyde(MDA).The study revealed a correlation between chlorophylls a and b content and the leaf pigmentation intensity–parameter a*.Addition of 1 mM ascorbic acid with 0.05 mM gibberellic acid into the MS medium plays a protective role in salinity tolerance by improving the shoot growth and the development as well as increasing the activities of the antioxidant enzymes and other antioxidant substances.

Brassinosteroids and Plant Responses to Heavy Metal Stress. An Overview

Soil contamination with heavy metals has become a world-wide problem, leading to the loss in agricultural productivity. Plants have a remarkable ability to take up and accumulate heavy metals from their external environment and it is well known that high levels of heavy metals affect different physiological and metabolic processes. Brassinosteroids are considered as the sixth class of plant hormones and they are essential for plant growth and development. These compounds are able of inducing abiotic stress tolerance in plants. In this paper, information about brassinosteroids and plant responses to heavy metal stress is reviewed.

REGENERATION FACTOR 1, a peptide boost for wound healing and plant biotechnology

Plants respond to wounding such as caused by insect herbivores by activating their defenses and thus increasing their resistance against attacking pests and opportunistic pathogens(Howe and Schaller,2008).The phenomenon was first described more than 50 years ago by Green and Ryan,who reported that wounding triggers tomato and potato plants to produce proteinase inhibitors that inhibit digestive proteases in the gut of leaf-eating insects to starve them of nutrients(Green and Ryan,1972).They also observed that the accumulation of proteinase inhibitors is not restricted to wounded leaves but occurs throughout the aerial parts of the plants.The search for a chemical signal that is released locally in response to wounding and that mediates systemic activation of defense gene expression led to the identification of systemin,the first ever peptide with hormonelike activity in plants(Pearce et al.,1991).These seminal findings sparked much research into systemic defense responses and peptide signaling in general,and we know now that systemin is one of many phytocytokines that regulate a multitude of immune responses in plants(Schilmiller and Howe,2005;Gust et al.,2017).

Patterns and Timing in Expression of Early Auxin-Induced Genes Imply Involvement of Phospholipases A （pPLAs） in the Regulation of Auxin Responses

While it is known that patatin-related phospholipase A （pPLA） activity is rapidly activated within 3min by auxin, hardly anything is known about how this signal influences downstream responses like transcription of early auxin-induced genes or other physiological responses. We screened mutants with T-DNA insertions in members of the pPLA gene family for molecular and physiological phenotypes related to auxin. Only one in nine Arabidopsis thaliana ppla knockdown mutants displayed an obvious constitutive auxin-related phenotype. Compared to wild-type, ppla-IIlδ mutant seedlings had decreased main root lengths and increased lateral root numbers. We tested auxin-induced gene expression as a molecular readout for primary molecular auxin responses in nine ppla mutants and found delayed up- regulation of auxin-responsive gene exRression in all of themL Thirty minutes after auxin treatment, up-regulation of up to 40% of auxin-induced genes was delayed in mutant seedlings. We observed only a few cases with hypersensitive auxin-induced gene expression in ppla mutants. While, in three ppla mutants, which were investigated in detail, rapid up- regulation （as early as 10 min after auxin stimulus） of auxin-regulated genes was impaired, late transcriptional responses were wild-type-like. This regulatory or dynamic phenotype was consistently observed in different ppla mutants with delayed up-regulation that frequently affected the same genes. This defect was not affected by pPLA transcript levels which remained constant. This indicates aposttranslational mechanism as a functional link of pPLAs to auxin signaling. The need for a receptor triggering an auxin response without employing transcription regulation is discussed.

Analysis of the plasmodesmatal proteins in higher plants

Gap junctions and plasmodesmata are the major structures in maintaining the entity of organisms. They play an very important role in regulating and controlling the cell proliferation, tissue metabolism and orchestration. Although gap junctions and plasmodesmata appear to be very dissimilar, they have a number of functional similarities. Gap junctions have been studied intensively and isolated successfully from numerous tissues and sources. In contrast, until recently very little was known about the biochemical composition of plasmodesmata and especially about the proteins that are involved in gating process. They have not yet been isolated and characterized.

Egg cell-secreted aspartic proteases ECS1/2 promote gamete attachment to prioritize the fertilization of egg cells over central cells in Arabidopsis

Double fertilization is an innovative phenomenon in angiosperms,in which one sperm cell first fuses with the egg cell to produce the embryo,and then the other sperm fuses with the central cell to produce the endosperm.However,the molecular mechanism of the preferential fertilization of egg cells is poorly understood.In this study,we report that two egg cell-secreted aspartic proteases,ECS1 and ECS2,play an important role in promoting preferential fertilization of egg cells in Arabidopsis.We show that simultaneous loss of ECS1 and ECS2 function resulted in an approximately 20%reduction in fertility,which can be complemented by the full-length ECS1/2 but not by corresponding active site mutants or by secretion-defective versions of ECS1/2.Detailed phenotypic analysis revealed that the egg cellsperm cell attachment was compromised in ecs1 ecs2 siliques.Limited pollination assays with cyclin-dependent kinase a1(cdka;1)pollen showed that preferential egg cell fertilization was impaired in the ecs1 ecs2 mutant.Taken together,these results demonstrate that egg cells secret two aspartic proteases,ECS1 and ECS2,to facilitate the attachment of sperm cells to egg cells so that preferential fertilization of egg cells is achieved.This study reveals the molecular mechanism of preferential fertilization in Arabidopsis thaliana.