Marková Hana, Tarkowská Danuše, Čečetka Petr, Kočová Marie, Rothová Olga, Holá Dana
Department of Genetics and Microbiology, Faculty of Science, Charles University, Prague, Czechia.
Laboratory of Growth Regulators, Centre of the Region Haná for Biotechnological and Agricultural Research, Institute of Experimental Botany, Czech Academy of Sciences, v.v.i. and Palacký University, Olomouc, Czechia.
Front Plant Sci. 2023 Jun 2;14:1139162. doi: 10.3389/fpls.2023.1139162. eCollection 2023.
Exogenously applied brassinosteroids (BRs) improve plant response to drought. However, many important aspects of this process, such as the potential differences caused by different developmental stages of analyzed organs at the beginning of drought, or by BR application before or during drought, remain still unexplored. The same applies for the response of different endogenous BRs belonging to the C, C-and C- structural groups to drought and/or exogenous BRs. This study examines the physiological response of two different leaves (younger and older) of maize plants exposed to drought and treated with 24-brassinolide (BL), together with the contents of several C, C-and C-BRs. Two timepoints of BL application (prior to and during drought) were utilized to ascertain how this could affect plant drought response and the contents of endogenous BRs. Marked differences in the contents of individual BRs between younger and older maize leaves were found: the younger leaves diverted their BR biosynthesis from C-BRs to C-BRs, probably at the very early biosynthetic steps, as the levels of C-BR precursors were very low in these leaves, whereas C-BR levels vere extremely high. Drought also apparently negatively affected contents of C-BRs (particularly in the older leaves) and C-BRs (particularly in the younger leaves) but not C-BRs. The response of these two types of leaves to the combination of drought exposure and the application of exogenous BL differed in some aspects. The older leaves showed accelerated senescence under such conditions reflected in their reduced chlorophyll content and diminished efficiency of the primary photosynthetic processes. In contrast, the younger leaves of well-watered plants showed at first a reduction of proline levels in response to BL treatment, whereas in drought-stressed, BL pre-treated plants they were subsequently characterized by elevated amounts of proline. The contents of C- and C-BRs in plants treated with exogenous BL depended on the length of time between this treatment and the BR analysis regardless of plant water supply; they were more pronounced in plants subjected to the later BL treatment. The application of BL before or during drought did not result in any differences of plant response to this stressor.
外源施加油菜素内酯（BRs）可改善植物对干旱的响应。然而，这一过程的许多重要方面，例如在干旱开始时被分析器官的不同发育阶段所导致的潜在差异，或者在干旱之前或期间施加BR所造成的差异，仍未得到探索。对于属于C、C-和C-结构组的不同内源BRs对干旱和/或外源BRs的响应情况也是如此。本研究考察了暴露于干旱并经24-表油菜素内酯（BL）处理的玉米植株的两片不同叶子（较幼嫩和较老的叶子）的生理响应，以及几种C、C-和C-BRs的含量。利用BL施加的两个时间点（干旱之前和干旱期间）来确定这如何影响植物对干旱的响应以及内源BRs的含量。发现较幼嫩和较老的玉米叶片中个别BRs的含量存在显著差异：较幼嫩的叶片可能在生物合成的非常早期阶段就将其BR生物合成从C-BRs转向了C-BRs，因为这些叶片中C-BR前体的水平非常低，而C-BR水平极高。干旱显然也对C-BRs（特别是在较老的叶片中）和C-BRs（特别是在较幼嫩的叶片中）的含量产生了负面影响，但对C-BRs没有影响。这两种类型的叶片对干旱暴露和外源BL施加的组合的响应在某些方面存在差异。较老的叶片在这种条件下表现出加速衰老，这体现在其叶绿素含量降低以及初级光合过程效率下降。相反，水分充足的植株的较幼嫩叶片在BL处理后起初脯氨酸水平降低，而在干旱胁迫且经BL预处理的植株中，它们随后的特征是脯氨酸含量升高。无论植物的水分供应情况如何，经外源BL处理的植株中C-和C-BRs的含量取决于该处理与BR分析之间的时间长度；在较晚进行BL处理的植株中更为明显。在干旱之前或期间施加BL并未导致植物对这种胁迫源的响应出现任何差异。
