Abstract
Balancing stomata-dependent CO2 assimilation and transpiration is a key challenge for increasing crop productivity and water use efficiency under drought stress for sustainable crop production worldwide. Here, we show that cucumber and luffa plants with luffa as rootstock have intrinsically increased water use efficiency, decreased transpiration rate and less affected CO2 assimilation capacity following drought stress over those with cucumber as rootstock. Drought accelerated abscisic acid (ABA) accumulation in roots, xylem sap and leaves, and induced the transcript of ABA signaling genes, leading to a decreased stomatal aperture and transpiration in the plants grafted onto luffa roots as compared to plants grafted onto cucumber roots. Furthermore, stomatal movement in the plants grafted onto luffa roots had an increased sensitivity to ABA. Inhibition of ABA biosynthesis in luffa roots decreased the drought tolerance in cucumber and luffa plants. Our study demonstrates that the roots of luffa have developed an enhanced ability to sense the changes in root-zone moisture and could eventually deliver modest level of ABA from roots to shoots that enhances water use efficiency under drought stress. Such a mechanism could be greatly exploited to benefit the agricultural production especially in arid and semi-arid areas.
Highlights
Increased water use efficiency (WUE) in various plant species[14,15,16,17]
We found that cucumber plants with luffa as rootstocks had an increased tolerance against drought as indicated by the increased biomass accumulation and decreased accumulation of ROS such as O2− and H2O2 under drought stress (Figs 1 and 7)
There was less accumulation of O2− and H2O2 whilst activity of several antioxidant enzymes was higher in the leaves of Cs/Lc plants as compared to Cs/Cs plants under drought (Fig. 1b and Supplementary Fig. S2)
Summary
Increased WUE in various plant species[14,15,16,17]. those transgenic plants showed reduced CO2 assimilation rate on which crop productivity largely depends. Recent studies have firmly established the role of the plant vascular system as an effective communication channel that transmits both root- and shoot-borne long-distance signals such as hormones under various abiotic and biotic conditions[18]. Selection of genotypes with appropriate ABA biosynthesis and sensitivity as well as enhanced drought tolerance remains as a challenge to the plant breeders[21] In this regard, grafting drought-sensitive genotype onto rootstock with increased ABA synthesis capacity or sensitivity in response to drought could be a useful approach to improve WUE and crop productivity. We compared the response of reciprocally grafted cucumber and luffa plants to drought stress through investigation of photosynthesis, transpiration, WUE and ABA signaling cascades. The mechanism of ABA-mediated drought tolerance in luffa rootstock- grafted cucumber was discussed
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