Differential Response to Heat Stress in Outer and Inner Onion Bulb Scales

First author: Ortal Galsurker; Affiliations: Agricultural Research Organization (以色列农业研究组织): Rishon LeZion, Israel

Corresponding author: Dani Eshel

Brown protective skin formation in onion bulbs (洋葱鳞茎) can be induced by rapid postharvest (采后) heat treatment. Onions that were peeled to different depths and were exposed to heat stress showed that only the outer scale formed dry brown skin, whereas the inner scales maintained high water content and did not change color. Our results reveal that browning of the outer scale during heat treatment is due to an enzymatic process that is associated with high levels of oxidation components, such as peroxidase (过氧化物酶) and quercetin glucoside (槲皮素葡糖苷). De-novo transcriptome analysis revealed differential molecular responses of the outer and inner scales to the heat stress. Genes involved in lipid metabolism (脂质代谢), oxidation pathways (氧化途径) and cell-wall modification were highly expressed in the outer scale during heating. Defense-response-related genes such as those encoding heat-shock proteins, antioxidative stress defense or production of osmoprotectant (渗透保护物) metabolites were mostly induced in the inner scale in response to the heat exposure. These transcriptomic data led to a conceptual (概念的) model that suggests sequential processes for browning development and desiccation (干燥) of the outer scales versus processes associated with defense response and heat tolerance in the inner scale. Thus, the observed physiological differences between the outer and inner scales is supported by the identified molecular differences.

洋葱球茎表面棕色的具有保护性质的表皮可以通过采后快速的热处理所诱导形成。洋葱可以剥落多层组织，在热处理的条件下，仅仅最外层形成棕色的表皮，内层仍然维持高水分含量的特性，且不改变颜色。本文的研究显示热处理条件下外层形成棕色表皮主要是源自于一些与氧化组分相关的酶促反应，比如过氧化物酶和槲皮素葡糖苷。转录组比较分析显示内层和外层在热处理下具有不同的分子响应通路。外层热处理条件下主要是参与脂质代谢、氧化途径和细胞壁修饰通路相关的基因高度上调表达，而内层响应热处理的则是防御响应相关的基因，如编码热激蛋白、抗氧化胁迫或渗透保护代谢物的基因。这些转录组的数据描绘了洋葱相对于内层响应热胁迫主要涉及一些防御响应和热耐受性相关的生物学进程，而外层则表现出棕色表皮发育和干燥的连续生物学进程的概念性模型。因此，本文所鉴定的分子层面的差异很好的解释了观察到的洋葱外层和内层生理上的差异。

通讯：Dani Eshel (http://www.agri.gov.il/people/239.aspx)

个人简介：1990-1993年，耶路撒冷希伯来大学，农学学士；1993-1995年，以色列农业研究中心（The Volcani Center），农学硕士；1996-2000年，以色列农业研究中心（The Volcani Center），农学博士。

研究方向：马铃薯采后的休眠解除及顶端优势；抑制贮藏块茎、根和鳞茎抽芽的方法；类Caspase蛋白在程序性细胞死亡中的作用；采后疾病防治。实验室网址：http://barakdror.wixsite.com/eshellab。

doi: https://doi.org/10.1093/jxb/ery189

Journal: Journal of Experimental Botany

Published date: 18 May, 2018

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