A role for brassinosteroids in the regulation of photosynthesis in Cucumis sativus

Abstract

The effects of 24-epibrassinolide (EBR) spray application on gas-exchange, chlorophyll fluorescence characteristics, Rubisco activity, and carbohydrate metabolism were investigated in cucumber (Cucumis sativus L. cv. Jinchun No. 3) plants grown in a greenhouse. EBR significantly increased the light-saturated net CO(2) assimilation rate (A(sat)) from 3 h to 7d after spraying, with 0.1 mg l(-1) EBR proving most effective. Increased A(sat) in EBR-treated leaves was accompanied by increases in the maximum carboxylation rate of Rubisco (V(c,max)) and in the maximum rate of RuBP regeneration (J(max)). EBR-treated leaves also had a higher quantum yield of PSII electron transport (phi(PSII)) than the controls, which was mainly due to a significant increase in the photochemical quenching (q(P)), with no change in the efficiency of energy capture by open PSII reaction centres (F'(v)/F'(m)). EBR did not influence photorespiration. In addition, significant increases in the initial activity of Rubisco and in the sucrose, soluble sugars, and starch contents were observed followed by substantial increases in sucrose phosphate synthase (SPS), sucrose synthase (SS), and acid invertase (AI) activities after EBR treatment. It was concluded that EBR increases the capacity of CO(2) assimilation in the Calvin cycle, which was mainly attributed to an increase in the initial activity of Rubisco.

Effect of Exogenous 24-Epibrassinolide on Salt Resistance of watermelon (Citrullus lanatus L.) under Salinity Stress

“…Similarly, no significant changes of Fv/Fm value in wheat, grown hydroponically in EBL-containing medium [14] or foliar sprayed [34] (Shahbaz et al, 2008). Yu [12] noted that EBL significantly increased the light saturated net CO2 assimilation rate from 3 h to7 d after spraying with 0.1 mg l -1 EBL in watermelon. Increased CO2 assimilation rate in EBL treated leaves was accompanied by a higher quantum yield of PSII electron transport, mainly due to a significant increase in the photochemical quenching and unchanged efficiency of energy capture by open PSII reaction centers [12] .…”

“…For example, Ali [14] reported that EBL increased growth in Indian mustard plants could be related to enhanced activity of antioxidative enzymes and proline level that protect the plants from oxidative damage. Therefore, photosynthesis which is a major controlling factor for plant growth and yield might have been increased due to EBL application [12] . In this study, foliar application of EBL enhanced CO2 assimilation rate in watermelon plants.…”

“…BRs promote plant growth through multiple mechanisms like cell division, cell elongation, vascular differentiation, germination, rhizogenesis, flowering, and modulation of gene expression [9] . Exogenous application of BRs promote leaf photosynthesis by positively regulating synthesis and activation of a variety of photosynthetic enzymes including Rubisco [10] , and this activity of BRs may contribute to increased crop yield after BRs application [11,12] . In addition to stimulating growth, BRs have an anti-stress effect on plants.…”

24-epibrassinolide regulated diminution of Cr metal toxicity in Brassica juncea L. plants

“…They are highly effective in stimulating growth in young vegetative tissues. Brassinosteroids promoted elongation of mung bean, soybean, pea epicotyls, bean, sunflower and cucumber hypocotyls, Arabidopsis peduncles and Hordeum vulgare seedlings (Gregory, 1982;Clouse et al, 1992;Yu et al, 2004;Clouse, 2008 andKartal et al, 2009). Hypocotyl elongation of Packchoi (Brassica chinensis) by brassinosteroids was reported (Wang et al, 1993) and application to apical 3-mm region gave the best effect.…”

“…Use of BRs has also been examined in agricultural production. Several studies have established that BRs influence seed germination, plant growth, nitrogen fixation, senescence, leaf abscission and enhanced tolerance against drought and cold stress, heavy metal stress, salt stress and diseases (Khripach et al, 2000;Anuradha and Rao, 2001;Nakashita et al, 2003;Yu et al, 2004). As a consequence, extensive research has been undertaken to develop BRs as plant growth regulators for agricultural production (Ikekawa and Zhao, 1991;Sasse, 2003;Ozdimer et al, 2004).…”