GhHSP24.7 mediates mitochondrial protein acetylation to regulate stomatal conductance in response to abiotic stress in cotton

During seed germination,the cotton chaperone protein HSP24.7 regulates the release,from the mitochondrial electron transport chain,of reactive oxygen species(ROS),a stimulative signal regulating germination.The function of HSP24.7 during vegetative stages remains largely unknown.Here we propose that suppression of Gh HSP24.7 in cotton seedlings increases tolerance to heat and drought stress.Elevation of Gh HSP24.7 was found to be positively associated with endogenous levels of ROS.We identified a new client protein of Gh HSP24.7,cotton lysine deacetylase(Gh HDA14),which is involved in mitochondrial protein modification.Elevated levels of Gh HSP24.7 suppressed deacetylase activity in mitochondria,leading to increased acetylation of mitochondrial proteins enriched in the subunit of Ftype ATPase,V-type ATPase,and cytochrome C reductase,ultimately reducing leaf ATP content.Consequently,in combination with altered ROS content,Gh HSP24.7 transgenic lines were unable to coordinate stomatal closure under stress.The regulation circuit composed of Gh HSP24.7 and Gh HDA14 represents a post-translation level mechanism in plant abiotic stress responses that integrates the regulation of ROS and ATP.

Stomatal Conductance, Growth and Yield of Pelargonium sidoides DC. in Response to Watering Frequency and Terminal Water Stress

Water is an important factor affecting growth, yield and distribution of different species. Plant response to water deficit can be in the form of physiological disorders, such as reduction in transpiration or assimilating partitioning to root growth. Sustainable use of water has become a priority in agriculture and thus innovative irrigation management practices are critical. The study aimed at investigating how watering frequency and terminal water stress influence growth of Pelargonium sidoides, an important medicinal plant in Southern Africa. The trial was a randomized complete block design with three replicates, and treatment factors were watering frequency （everyday, twice and once a week） and terminal water stress （no watering four weeks before harvesting, no watering two weeks before harvesting and no terminal stress）. There was an interacting effect of watering frequency and terminal water stress on biomass and fresh root yield. More frequent watering resulted in significantly higher biomass and fresh root yield, compared to other treatments. Watering everyday with terminal or no terminal water stress resulted in higher fresh root yield, compared to other watering treatments with terminal water stress. Plant height and leaf area were significantly affected by watering frequency and terminal water stress, respectively. A significant drop in stomatal conductance of plants watered everyday was observed 240 d after treatment implementation, such that there was no significant difference across all the three watering frequency treatments. In conclusion, farmers can save on irrigation costs by reducing watering frequency, as there was no significant difference on dry root yield.

Growth and Eco-Physiological Performance of Cotton Under Water Stress Conditions

A cotton cultivar Xinluzao 8 was grown under four levels of water stress treatments （normal irrigation, slight, mild and severe water stress） from the initial reproductive growth stage in Shihezi, Xinjiang, China, in 2002, to evaluate the growth and eco-physiological performances. Under water stress conditions, the transpiration ability decreased while the leaf temperature increased. Although the relative leaf water content decreased as water stress increased, the differences among the treatments were small, indicating that cotton has high ability in maintaining water in leaf. The stomatal density increased as water stress increased, while the maximum stomatal aperture reduced only in the severest stressed plants. The time of the maximum stomatal aperture was delayed in the mild and severe stressed plants. When severe stress occurred, the stomata were kept open until the transpiration decreased to nearly zero, suggesting that the stomata might not be the main factor in adjusting transpiration in cotton. Cotton plant has high adaptation ability to water stress conditions because of decrease in both stomatal conductance and hydraulic conductance from soil-to-leaf pathway. The actual quantum yield of photosystem Ⅱ （PS Ⅱ） decreased under water stress conditions, while the maximum quantum yield of PS Ⅱ did not vary among treatments, suggesting that PS II would not be damaged by water stress. The total dry weight reduced as water stress increased.

Flavonols Induced by 5-Aminolevulinic Acid Are Involved in Regulation of Stomatal Opening in Apple Leaves

Flavonols, the main flavonoids in plant leaves, have newly been proposed as a H2O2 scavenger in guard cells. However, whether 5-aminolevulinic acid(5-ALA) is involved in regulating stomatal movement of apple(Malus × domestica Borkh. ‘Fuji') leaves through flavonol accumulation remains unclear. In this study, using diphenylboric acid 2-amino ethyl ester(DPBA, a flavonol fluorescent dye) and a laser scanning confocal microscope,we observed that 5-ALA pretreatment significantly improved flavonol accumulation in guard cells of apple leaves, especially around the nucleus.Then we demonstrated that 5-ALA pretreatment inhibited ABA-induced stomatal closure via decreasing reaction oxygen species(ROS) accumulation in guard cells. Pretreatment with quercetin or kaempferol, two main kinds of flavonols in plants, also inhibited ABA-induced stomatal closure by decreasing ROS content in the guard cells. Furthermore, exogenous flavonols could suppress H2O2-induced stomatal closure in apple leaves.Taken together, we conclude that ALA-induced flavonol accumulation in guard cells is involved in the inhibitory effect of ALA on ABA-induced ROS accumulation and stomatal closure in apple leaves.