Abstract
Various biotic and abiotic stresses threaten the cultivation of future agricultural crops. Among these stresses, heat stress is a major abiotic stress that substantially reduces agricultural productivity. Many strategies to enhance heat stress tolerance of crops have been developed, among which is grafting. Here, we show that Momordica-grafted cucumber scions have intrinsically enhanced chlorophyll content, leaf area, and net photosynthetic rate under heat stress compared to plants grafted onto cucumber rootstock. To investigate the mechanisms by which Momordica rootstock enhanced cucumber scions heat stress tolerance, comparative proteomic analysis of cucumber leaves in response to rootstock-grafting and/or heat stress was conducted. Seventy-seven differentially accumulated proteins involved in diverse biological processes were identified by two-dimensional electrophoresis (2-DE) in conjunction with matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF MS). The following four main categories of proteins were involved: photosynthesis (42.8%), energy and metabolism (18.2%), defense response (14.3%), and protein and nucleic acid biosynthesis (11.7%). Proteomic analysis revealed that scions grafted onto Momordica rootstocks upregulated more proteins involved in photosynthesis compared to scions grafted onto cucumber rootstocks under heat stress and indicated enhanced photosynthetic capacity when seedlings were exposed to heat stress. Furthermore, the expression of photosynthesis-related genes in plants grafted onto Momordica rootstocks significantly increased in response to heat stress. In addition, increased high-temperature tolerance of plants grafted onto Momordica rootstock was associated with the accumulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and oxygen-evolving enhancer protein 1 (OEE1). Taken together, the data indicated that Momordica rootstock might alleviate growth inhibition caused by heat stress by improving photosynthesis, providing valuable insight into enhancing heat stress tolerance in the global warming epoch.
Highlights
Plant physiological processes are negatively affected by heat stress, and a crucial constraint for crop growth and productivity worldwide[1, 2]
Chlorophyll content, and net photosynthetic rate analysis To investigate the role of Momordica rootstock responses to heat stress, we compared the tolerance to heat stress of cucumber plants grafted onto cucumber rootstock to plants grafted onto Momordica rootstock
Dry weight, and leaf area of plants grafted onto cucumber rootstock were 0.85-fold, 0.81-fold, and 0.76-fold change of plants grafted onto Momordica rootstock respectively after 7 days of heat stress (Table 1)
Summary
Plant physiological processes are negatively affected by heat stress, and a crucial constraint for crop growth and productivity worldwide[1, 2]. The temperature in summer in the southern region of China usually exceeds 40 °C. High temperature induces leaf wilting, inhibits shoot and root growth, and results in decreased dry matter accumulation[3]. Photosynthesis is sensitive to temperature[4]. The enzymes for energy distribution and carbon metabolism, especially Rubisco, are significantly affected by heat stress[5]. Heat-tolerant varieties of crops have higher photosynthetic efficiency than heat-sensitive varieties when exposed to high temperature[6,7,8]. Photosynthesis is the physiological process that is sensitive to temperature[5]
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