Yarmolinsky Dmitry, Brychkova Galina, Kurmanbayeva Assylay, Bekturova Aizat, Ventura Yvonne, Khozin-Goldberg Inna, Eppel Amir, Fluhr Robert, Sagi Moshe
The Jacob Blaustein Institute for Desert Research, Albert Katz Department of Dryland Biotechnologies, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel (D.Y., G.B., A.K., A.B., Y.V., I.K.-G., A.E., M.S.); andDepartment of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel (R.F.).
The Jacob Blaustein Institute for Desert Research, Albert Katz Department of Dryland Biotechnologies, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel (D.Y., G.B., A.K., A.B., Y.V., I.K.-G., A.E., M.S.); andDepartment of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel (R.F.)
Plant Physiol. 2014 Aug;165(4):1505-1520. doi: 10.1104/pp.114.241356. Epub 2014 Jul 1.
Sulfite reductase (SiR) is an essential enzyme of the sulfate assimilation reductive pathway, which catalyzes the reduction of sulfite to sulfide. Here, we show that tomato (Solanum lycopersicum) plants with impaired SiR expression due to RNA interference (SIR Ri) developed early leaf senescence. The visual chlorophyll degradation in leaves of SIR Ri mutants was accompanied by a reduction of maximal quantum yield, as well as accumulation of hydrogen peroxide and malondialdehyde, a product of lipid peroxidation. Interestingly, messenger RNA transcripts and proteins involved in chlorophyll breakdown in the chloroplasts were found to be enhanced in the mutants, while transcripts and their plastidic proteins, functioning in photosystem II, were reduced in these mutants compared with wild-type leaves. As a consequence of SiR impairment, the levels of sulfite, sulfate, and thiosulfate were higher and glutathione levels were lower compared with the wild type. Unexpectedly, in a futile attempt to compensate for the low glutathione, the activity of adenosine-5'-phosphosulfate reductase was enhanced, leading to further sulfite accumulation in SIR Ri plants. Increased sulfite oxidation to sulfate and incorporation of sulfite into sulfoquinovosyl diacylglycerols were not sufficient to maintain low basal sulfite levels, resulting in accumulative leaf damage in mutant leaves. Our results indicate that, in addition to its biosynthetic role, SiR plays an important role in prevention of premature senescence. The higher sulfite is likely the main reason for the initiation of chlorophyll degradation, while the lower glutathione as well as the higher hydrogen peroxide and malondialdehyde additionally contribute to premature senescence in mutant leaves.
亚硫酸盐还原酶（SiR）是硫酸盐同化还原途径中的一种关键酶，它催化亚硫酸盐还原为硫化物。在此，我们表明，由于RNA干扰导致SiR表达受损的番茄（Solanum lycopersicum）植株出现了早期叶片衰老现象。SIR Ri突变体叶片中可见的叶绿素降解伴随着最大量子产率的降低，以及过氧化氢和脂质过氧化产物丙二醛的积累。有趣的是，与野生型叶片相比，突变体中叶绿体中参与叶绿素分解的信使RNA转录本和蛋白质水平升高，而在光系统II中发挥作用的转录本及其质体蛋白水平降低。由于SiR功能受损，与野生型相比，亚硫酸盐、硫酸盐和硫代硫酸盐的水平更高，而谷胱甘肽水平更低。出乎意料的是，为了徒劳地补偿低水平的谷胱甘肽，腺苷-5'-磷酸硫酸还原酶的活性增强，导致SIR Ri植株中亚硫酸盐进一步积累。亚硫酸盐氧化为硫酸盐的增加以及亚硫酸盐掺入磺基喹喔基二酰基甘油不足以维持低水平的基础亚硫酸盐，导致突变体叶片累积性损伤。我们的结果表明，除了其生物合成作用外，SiR在预防早衰中也起着重要作用。较高的亚硫酸盐可能是叶绿素降解起始的主要原因，而较低的谷胱甘肽以及较高的过氧化氢和丙二醛也加剧了突变体叶片的早衰。
