Target-Based Physiological Modulations and Chloroplast Proteome Reveals a Drought Resilient Rootstock in Okra (Abelmoschus esculentus) Genotypes

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.

Proteomic Analysis Revealed Different Molecular Mechanisms of Response to PEG Stress in Drought-Sensitive and Drought-Resistant Sorghums

“…Under drought stress, the total chlorophyll content in the leaves of the four varieties decreased, and the reduction in the chlorophyll content in the drought-resistant sorghums (T14: 9.32% and T33: 9.23%) was less than that in drought-sensitive sorghums (S4: 14.26% and S4-1: 11.95%) ( Figure 2 C), indicating that drought-resistant sorghum showed strong adaptability to drought stress and higher photosynthetic efficiency to maintain growth. This is consistent with the gradual decrease in chlorophyll content in Abelmoschus esculentus under drought stress [ 25 ].…”

Grafting enhances drought tolerance by regulating and mobilizing proteome, transcriptome and molecular physiology in okra genotypes

“…The experiment was arranged in a completely randomized design (CRD) such that each treatment had five replicates. Three combinations of grafted plants were prepared: NS7772 grafted onto NS7774 (G1), green gold grafted onto NS7774 (G2) and lastly OH3312 grafted onto NS7774 (G3) as NS7774 is the drought tolerant rootstock as previously studied (Razi et al, 2021).The seeds were sown at the appropriate planned time, so that once the vegetative stage arrived, 25-30 days after date of sowing and if the rootstock was vigorous enough then grafting was carried out in the early morning timings using cleft grafting method (Supplementary Figure 3). All the homograft was covered with transparent plastic to maintain the humidity at 90%-95% and temperature at ∼25-28°C to accelerate the healing process and avoid water loss.…”

“…The structure of stomata was visualized under high power magnification by using compound microscope. The same samples were used for stomatal index determination as described previously (Razi et al, 2021).…”

“…The H 2 O 2 standard curve was utilised to determine its concentration. Malondialdehyde content (MDA) content was performed as described previously (Razi et al, 2021). The protocol described by Lutts et al, 1996 served as the basis to calculate the percentage of electrolyte leakage.…”

Recent Advances in Okra Responses to Drought

“…In addition, different cultivars exhibit a wide range of drought tolerance (Abd El-Fattah et al, 2019). Thus, the drought-induced drop in okra is also dependent on the cultivar (Razi et al, 2021).…”