Abstract
As climate changes increase, drought stress is becoming a problem for all major horticultural crops; among them is okra (Abelmoschus esculentus). Despite its superior resilience to heat stress and high nutritional content, it is still underutilized in contrast to other vegetable crops. Moreover, the drought-resistant and drought-sensitive genotypes of okra are also not well known and require further exploration to improve their productivity. To investigate this in more detail, we performed comparative physiological and large-scale chloroplast proteomics on drought-stressed genotypes of okra. We evaluated four major genotypes of okra, viz., NS7774, NS7772, Green Gold, and OH3312 for drought resilient rootstock. The physiological modulations demonstrated a significant change by 50–76% in biomass, net-photosynthetic machinery, water transport, and absorption both in early and late stages of drought stress compared to well-watered crops in all genotypes. Maximum oxidative damage due to drought stress was observed for the genotypes NS7772, Green Gold and OH3312 as depicted by H2O2 and O2− determination. Greater oxidative stress was correlated to lesser antioxidant activity and expression of antioxidant enzymes, such as catalase and ascorbate peroxidase under stress in okra genotypes. The overall photosynthetic pigments, such as total chlorophyll, and total carotenoid content, were also decreased, and stomatal guard cells were disrupted and appeared closed compared to the control for the above three mentioned genotypes, except NS7774. A subsequent tissue-specific proteome analysis of chloroplasts and thylakoids analyzed by BN-PAGE (blue native polyacrylamide gel electrophoresis) revealed either over or under expression of specific proteins, such as ATPase, PSI, PSII core dimer, PSII monomer and ATP synthase. The expression of multiprotein complex proteins, including PSII-core dimer and PSII-core monomer, was slightly higher for the genotype NS7774 when compared to three other genotypes for both 5 and 10 days of drought stress. Further identification of specific proteins obtained in second dimension BN-PAGE provided descriptive detail of seven proteins involved in drought resistance across all genotypes. The identified proteins are majorly involved in photosynthesis under drought stress, suggesting NS7774 as a drought tolerant genotype. Further, the proteomic results were confirmed using Immunoblot by selecting specific protein such as PsaA. Overall, from our physiological modulations and chloroplast proteomics in all genotypes, we summarized NS7774 as a resilient rootstock and the other three genotypes (NS7772, OH3312, and Green Gold) as sensitive ones.
Highlights
Drought stress is one of the major environmental stresses that affects plant growth, survival, and production [1,2]
The chloroplast, which is the organelle responsible for photosynthesis, becomes affected, because it is highly sensitive to drought stress, which results in a generation of more reactive oxygen species (ROS), decreasing the chlorophyll synthesis, quantum yield, and efficiency of light-harvesting complexes (LHC) I and II, which decrease the health and viability of the plant [14]
D5i)ffehreancdes alimtotnlgeaillmtrepatmaecnttsowneretdheteermminoedrpholo using a two-way analysis of variance followed by a Student’s t-test with p < 0.05 as the genotypes of oklirmait(oNf siSgn7ifi7c7an4c,e.NS7772, Green Gold, and OH3312) (Figure 1), wh icant changes w3. eRerseultos bserved at later stages of drought stress
Summary
Drought stress is one of the major environmental stresses that affects plant growth, survival, and production [1,2]. The initial response of plants includes poor germination [6,7,8]. Whereas severe drought stress results in impaired growth of the plants and reduced biomass, height, leaf size, and stem girth [9,10,11]. The chloroplast, which is the organelle responsible for photosynthesis, becomes affected, because it is highly sensitive to drought stress, which results in a generation of more reactive oxygen species (ROS), decreasing the chlorophyll synthesis, quantum yield, and efficiency of light-harvesting complexes (LHC) I and II, which decrease the health and viability of the plant [14]. It is very important to study the effect of drought stress on the chloroplast proteome of vegetables to provide solutions for improved plant growth
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