Abstract
Calcium and ethylene are essential in plant growth and development. In this study, we investigated the effects of calcium and ethylene on adventitious root formation in cucumber explants under salt stress. The results revealed that 10 μM calcium chloride (CaCl2) or 0.1 μM ethrel (ethylene donor) treatment have a maximum biological effect on promoting the adventitious rooting in cucumber under salt stress. Meanwhile, we investigated that removal of ethylene suppressed calcium ion (Ca2+)-induced the formation of adventitious root under salt stress indicated that ethylene participates in this process. Moreover, the application of Ca2+ promoted the activities of 1-aminocyclopropane-l-carboxylic acid synthase (ACS) and ACC Oxidase (ACO), as well as the production of 1-aminocyclopropane-l-carboxylic acid (ACC) and ethylene under salt stress. Furthermore, we discovered that Ca2+ greatly up-regulated the expression level of CsACS3, CsACO1 and CsACO2 under salt stress. Meanwhile, Ca2+ significantly down-regulated CsETR1, CsETR2, CsERS, and CsCTR1, but positively up-regulated the expression of CsEIN2 and CsEIN3 under salt stress; however, the application of Ca2+ chelators or channel inhibitors could obviously reverse the effects of Ca2+ on the expression of the above genes. These results indicated that Ca2+ played a vital role in promoting the adventitious root development in cucumber under salt stress through regulating endogenous ethylene synthesis and activating the ethylene signal transduction pathway.
Highlights
Calcium ion (Ca2+), which is a versatile signaling ion, has been confirmed to play an essential role in plant growth [1,2] and development [3,4,5]
There is little research regarding the relationship between calcium and ethylene on adventitious root formation under salt stress
Some researches demonstrated that the concentration of CaCl2 in μM range significantly promoted adventitious rooting, which implied that Ca included in the μM range could have an obvious effect on regulating adventitious root development [11,49] Previously, Ca2+ has been demonstrated to induce the adventitious rooting of cucumber under abiotic stress
Summary
Calcium ion (Ca2+), which is a versatile signaling ion, has been confirmed to play an essential role in plant growth [1,2] and development [3,4,5]. Higher concentrations of CaCl2 (50, 100, and 1000 μM) significantly decreased the root number and root length, which indicates that the effect of Ca2+ on root number and root length of adventitious roots was dose-dependent under salt stress. Since 0.1 μM ethrel achieved maximum biological effect during adventitious root formation under salt stress, we used 0.1 μM of ethylene for subsequent length of cucumber explant treated with 0.1 μM ethrel. To investigate whether exogenous Ca2+ will affect endogenous ethylene content on adventitious root development in cucumber explants under salt stress, we used the calcium channel inhibitor LaCl3 and calcium chelator methylene glycol-bis (2-aminoethylether) -N,N,N ,N -tetraacetic acid (EGTA) to study their effect on ACS activity, ACO activity, ACC production, and ethylene production in different stages. LaCl3 and EGTA could significantly decrease the expression of CsEIN2 and CsEIN3 under salt stress, while LaCl3 + CaCl2 and EGTA + CaCl2 markedly up-regulated the expression of CsEIN2 as compared with LaCl3 and EGTA, but for CsEIN3 under salt stress
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