Abstract

Uniconazole (S-(+)-uniconazole), a plant growth retardant, exerts key roles in modulating growth and development and increasing abiotic stress tolerance in plants. However, the underlying mechanisms by which uniconazole regulates drought response remain largely unknown. Here, the effects of exogenous uniconazole on drought tolerance in hemp were studied via physiological and transcriptome analyses of the drought-sensitive industrial hemp cultivar Hanma No. 2 grown under drought stress. Exogenous uniconazole treatment increased hemp tolerance to drought-induced damage by enhancing chlorophyll content and photosynthesis capacity, regulating activities of enzymes involved in carbon and nitrogen metabolism, and altering endogenous hormone levels. Expression of genes associated with porphyrin and chlorophyll metabolism, photosynthesis-antenna proteins, photosynthesis, starch and sucrose metabolism, nitrogen metabolism, and plant hormone signal transduction were significantly regulated by uniconazole compared with that by control (distilled water) under drought stress. Numerous genes were differentially expressed to increase chlorophyll content, enhance photosynthesis, regulate carbon–nitrogen metabolism-related enzyme activities, and alter endogenous hormone levels. Thus, uniconazole regulated physiological and molecular characteristics of photosynthesis, carbon–nitrogen metabolism, and plant hormone signal transduction to enhance drought resistance in industrial hemp.

Highlights

  • Drought stress, an abiotic stress, has more important effects on crop yield and quality compared to other abiotic stresses, inducing a highly vulnerable state in plants because of high temperature and low water ­content[1]

  • Our finding that photosynthetic rate (PN) was reduced in the leaves of industrial hemp seedlings under drought stress (Fig. 1e) was similar to that documented by Jhou et al.[26]

  • The expression of genes corresponding to glutamyl-tRNA reductase, Mg chelatase subunit, Mg protoporphyrin IX monomethyl ester cyclase, protochlorophyllide reductase, and Chlorophyll(ide) b reductase were regulated by uniconazole under drought stress (Fig. 6a, Supplementary Table S2)

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Summary

Introduction

An abiotic stress, has more important effects on crop yield and quality compared to other abiotic stresses, inducing a highly vulnerable state in plants because of high temperature and low water ­content[1]. The activities of key enzymes involved in N metabolism may play a major role in plant photosynthetic adaptation under drought s­ tress[6]. Uniconazole has various functions in promoting proline and soluble sugar accumulation, strengthening the antioxidant defence system, stimulating protein levels and nitrate reductase (NR) activity, and altering endogenous hormone levels These experiments were conducted for different plants, such as soybean, bean, winter rape, and datura. Research in other plants has revealed that uniconazole produces a marked effect on plant hormone metabolism It induced a reduction in the content of gibberellin-like substances, mainly by inhibiting the cytochrome P450 enzyme ent-kaurene oxidase, which catalyses the three oxidation steps of transformation from ent-kaurene to ent-kaurenoic ­acid[19]. The genes and metabolic pathways involved in the response of hemp to uniconazole treatment under drought stress are unknown. Our findings potentially lead to a thorough understanding of the biological function and the molecular mechanisms underlying uniconazole activity in hemp under drought stress

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