Phytochromes are plant photoreceptors that have long been associated with photomorphogenesis in plants; however, more recently, their crucial role in the regulation of variety of abiotic stresses has been explored. Chilling stress is one of the abiotic factors that severely affect growth, development, and productivity of crops. In the present work, we have analyzed and compared physiological, biochemical, and molecular responses in two contrasting phytochrome mutants of tomato, namely aurea (aur) and high pigment1 (hp1), along with wild-type cultivar Micro-Tom (MT) under chilling stress. In tomato, aur is phytochrome-deficient mutant while hp1 is a phytochrome-sensitive mutant. The genotype-specific physiological, biochemical, and molecular responses under chilling stress in tomato mutants strongly validated phytochrome-mediated regulation of abiotic stress. Here, we demonstrate that phytochrome-sensitive mutant hp1 show improved performance compared to phytochrome-deficient mutant aur and wild-type MT plants under chilling stress. Interestingly, we noticed significant increase in several photosynthetic-related parameters in hp1 under chilling stress that include photosynthetic rate, stomatal conductance, stomatal aperture, transpiration rate, chlorophyll a and carotenoids. Whereas most parameters were negatively affected in aur and MT except a slight increase in carotenoids in MT plants under chilling stress. Further, we found that PSII quantum efficiency (Fv/Fm), PSII operating efficiency (Fq′/Fm′), and non-photochemical quenching (NPQ) were all positively regulated in hp1, which demonstrate enhanced photosynthetic performance of hp1 under stress. On the other hand, Fv/Fm and Fq′/Fm′ were decreased significantly in aur and wild-type plants. In addition, NPQ was not affected in MT but declined in aur mutant after chilling stress. Noticeably, the transcript analysis show that PHY genes which were previously reported to act as molecular switches in response to several abiotic stresses were mainly induced in hp1 and repressed in aur and MT in response to stress. As expected, we also found reduced levels of malondialdehyde (MDA), enhanced activities of antioxidant enzymes, and higher accumulation of protecting osmolytes (soluble sugars, proline, glycine betaine) which further elaborate the underlying tolerance mechanism of hp1 genotype under chilling stress. Our findings clearly demonstrate that phytochrome-sensitive and phytochrome-deficient tomato mutants respond differently under chilling stress thereby regulating physiological, biochemical, and molecular responses and thus establish a strong link between phytochromes and their role in stress tolerance.

中文翻译：

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对番茄的两个植物色素突变体（Micro-Tom cv。）的比较分析揭示了低温胁迫下的特定生理，生化和分子响应

植物色素是植物的光感受器，长期以来与植物的光形态发生有关。然而，最近，已经探索了它们在调节多种非生物胁迫中的关键作用。低温胁迫是严重影响农作物生长，发育和生产力的非生物因素之一。在目前的工作中，我们已经分析并比较了两种不同的番茄植物色素突变体，即金黄色葡萄球菌（aur）和高色素1（hp1），以及野生型栽培品种Micro-Tom（MT）的生理，生化和分子响应。令人不寒而栗。在番茄中，aur是植物色素缺乏的突变体，而hp1是植物色素敏感的突变体。基因型特定的生理，生化，番茄突变体在低温胁迫下的分子响应和分子反应强烈验证了植物色素介导的非生物胁迫调控。在这里，我们证明，在低温胁迫下，与植物色素缺乏的突变体aur和野生型MT植物相比，植物色素敏感的突变体hp1表现出更高的性能。有趣的是，我们注意到hp1在低温胁迫下与光合作用相关的参数显着增加，包括光合速率，气孔导度，气孔孔径，蒸腾速率，叶绿素a和类胡萝卜素。而大多数参数在aur和MT中均受到不利影响，除了在低温胁迫下MT植物中类胡萝卜素的含量略有增加。此外，我们发现PSII量子效率（Fv / Fm），PSII工作效率（Fq'/ Fm'），和非光化学淬灭（NPQ）在hp1中均受到正调控，这表明hp1在胁迫下的光合性能增强。另一方面，在aur和野生型植物中Fv / Fm和Fq'/ Fm'显着降低。此外，NPQ不受MT影响，但在寒冷胁迫后aur突变体中NPQ下降。值得注意的是，转录本分析表明，以前据报道可响应几种非生物胁迫而充当分子开关的PHY基因主要是在hp1中诱导的，而在aur和MT中则是对胁迫的抑制。正如预期的那样，我们还发现丙二醛（MDA）含量降低，抗氧化酶活性增强以及保护性渗透剂（可溶性​​糖，脯氨酸，甘氨酸甜菜碱），进一步阐明了寒冷胁迫下hp1基因型的潜在耐受机制。我们的发现清楚地表明，对植物色素敏感和缺乏植物色素的番茄突变体在低温胁迫下具有不同的反应，从而调节生理，生化和分子反应，从而在植物色素及其在胁迫耐受性中的作用之间建立了牢固的联系。