Senescence-specific Changes in Endogenous IAA Content and Its Conjugated Status in Rice Flag Leaf as Affected by Nitrogen Level

doi:10.16819/j.1001-7216.2018.8028

Abstract

Abstract:

【Objective】 The objective is to clarify the genotype-dependent alteration in rice leaf senescence process and its relationship with the endogenous IAA content and its conjugated status in flag leaves during filling stage, and also to investigate the effect of N supply levels on leaf senescence and its relation to the endogenous IAA content and its conjugated status in leaves for different rice genotypes. 【Method】 Two rice genotypes, namely, the premature senescence mutant in flag leaf (psf) and its wild type (Zhehui 7954), were used to compare their difference in the temporal patterns of IAA content and its conjugated status as well as transcriptional expression of YUCCAs family genes in flag leaf during filling stage. Three N levels, including low nitrogen level (LN, 1.45 mmol/L), normal nitrogen level (MN, 2.9 mmol/L), and high nitrogen level (HN, 5.8 mmol/L), were designed to examine the response of IAA content and its conjugated status in senescent leaves to different N supply levels. 【Result】The free IAA content in the flag leaf of psf mutant was significantly lower than that of its wild type during leaf senescence, while the opposite was true for the genotype-dependent alteration in the conjugated status IAA (IAA-ASP) content in senescent leaves, with a markedly higher level and more rapidly increase of IAA-ASP content in the flag leaf of psf mutant relative to its wild type along with leaf senescence. Among 7 YUCCAs isoform genes related to IAA biosynthesis, the transcriptional expressions of YUCCA2, YUCCA3, YUCCA4 and YUCCA6 were relatively lower in the flag leaf of psf mutant compared with its wild type, with the down-regulated temporal pattern during leaf senescence, regardless of rice genotypes. However, the transcript amount of YUCCA7 in senescent leaves increased markedly from 0 to 21 days post anthesis, followed by a declining level of transcriptional expression at the late stage of leaf senescence process. This result implied that the rapid decrease in chlorophyll contents and also its accelerated leaf senescence symptoms for psf mutant were partly attributable to the weaker IAA biosynthesis in psf leaves during leaf senescence, in which the transcriptional level of YUCCA7 expression might play an important role in the regulation of IAA biosynthesis in senescent leaves; the effect of N supply on the endogenous IAA content and its conjugated status in rice leaves was greatly variable, depending on the stage of leaf senescence. At the initial and early stages of leaf senescence, LN treatment decreased the free-IAA content in rice leaves and increased the IAA-ASP content in rice leaves, while HN resulted in a marked increase in free-IAA content in the senescent leaves, with a significant decrease in IAA-ASP content under HN. Comparatively, HN treatment displayed lower level in both free-IAA and IAA-ASP contents than NN an LN treatment at the late stage of leaf senescence (for psf mutant at about 28 day post anthesis) with severe leaf senescence symptom【Conclusion】The onset and progression of leaf senescence were closely associated with IAA content and its conjugated status in rice leaves. The markedly increased IAA-ASP content in rice leaves may be considered as one of most important reasons for the accelerating progression of leaf senescence symptom, and HN-induced decrease in IAA-ASP content in rice leaves was, at least partly, responsible for the delay of leaf senescence progression.

Key words: Oryza sativa, leaf senescence, auxin (IAA), nitrogen supply, psf mutant

摘要：

目的揭示水稻抽穗开花后剑叶衰老过程的内源自由态IAA和轭合态IAA含量的动态变化及其基因型间的差异,明确氮素营养供应对叶片衰老过程的延缓效应及其与两种化学态IAA含量之间的关系。方法以剑叶早衰水稻突变体(psf)与其野生型(浙恢7954)为材料,比较了其在大田条件下剑叶衰老过程中的内源IAA含量、IAA类型和YUCCAs家族基因转录表达量差异,并利用水培种植试验设低氮(LN, 1.45 mmol/L)、正常氮(NN, 2.9 mmol/L)和高氮(HN, 5.8 mmol/L)3个氮浓度水平处理,对不同氮素水平下水稻叶片衰老相关指标与两类IAA含量间的关系进行了分析。结果早衰突变体psf剑叶中的自由态IAA含量显著低于相同取样时期的野生对照,但前者剑叶中的轭合态IAA含量显著高于后者,且随叶片衰老进程呈较明显的上升趋势;在7个YUCCAs同工型基因中,YUCCA1、YUCCA2、YUCCA3、YUCCA4和YUCCA6)的转录表达量随叶片衰老而下降,但YUCCA7则随叶片衰老呈现出先上升后下降的变化趋势。相同灌浆时期相比,绝大多数YUCCAs在早衰突变体psf剑叶中的转录表达量要低于其野生型对照,说明IAA合成代谢较弱是psf剑叶叶绿素含量迅速下降和早衰症状加剧的重要原因之一。其中,YUCCA7转录表达量随叶片衰老而上升,可能对psf已衰老叶片中的IAA合成起重要调控作用;氮浓度对水稻叶片中的IAA含量及其自由态与共轭态的影响表现为,在叶片开始衰老的初期和前中期,低氮处理(LN)引起剑叶中的自由态IAA含量下降和轭合态IAA含量上升,而高氮处理(HN)可诱导叶片中的自由态IAA含量增加,并导致轭合态IAA含量明显降低,但对已严重衰老的叶片而言(psf在抽穗开花后28 d的剑叶),高氮处理下(HN)的自由态IAA和轭合态IAA含量均低于正常氮处理(NN)和低氮处理(LN)。结论水稻叶片的衰老进程与其叶片器官中的IAA含量及其化学态之间存在较密切联系。其中,轭合态IAA含量在叶片衰老过程的大幅度提升,是早衰突变体psf 剑叶衰老进程加快的一个重要生理特征,而轭合态IAA含量的下降,可能是高氮处理对水稻叶片衰老进程起到延缓作用的一个重要生理调节因素。

关键词: 水稻, 叶片衰老, 生长素, 氮素营养, 早衰突变体

CLC Number:

Hua ZHAO, Fubiao WANG, Zhanyu HAN, zakari SHAMSU-ADO, Zhaowei LI, Gang PAN, Fangmin CHENG. Senescence-specific Changes in Endogenous IAA Content and Its Conjugated Status in Rice Flag Leaf as Affected by Nitrogen Level[J]. Chinese Journal OF Rice Science, 2018, 32(6): 591-600.

赵华, 王复标, 韩展誉, SHAMSU-ADOzakari, 李兆伟, 潘刚, 程方民. 水稻剑叶衰老过程中内源IAA的轭合态变化及其氮素调控效应[J]. 中国水稻科学, 2018, 32(6): 591-600.

Figures/Tables 5

Fig. 1. Difference in plant type and leaf appearance between psf mutant and its wild type (Zhehui 7954) at different growth stages.^ A, Tillering stage (left, wild type; right, psf mutant); B, Heading and flowering stage (left, wild type; right, psf mutant ); C, Phenotype of the flag leaf of psf and its wild type during filling stage (7, 14, 21 and 28 days after heading, from left to right, respectively).

Table 1 Sequence of primer pairs used for real-time quantitative PCR in this study.

基因名称 Gene name	登录号 Accession No.	引物 Primer pairs(5'-3')	产物大小 Product size/ bp
Actin	X16280	CAGCACATTCCAGCAGATGT TAGGCCGGTTGAAAACTTTG	198
YUCCA1	LOC_Os01g45760	TTGGATTTGTGCCGGCATGG TCGACGAGCTGAACCGGTAG	140
YUCCA2	LOC_Os05g45240	GCGCAGAATTTGACGAGCGA ACCAGCCACTGCGACACATA	100
YUCCA3	LOC_Os01g53200	GGCTCTACTCGGTCGGGTTC GCTTCCCTCTGGCCTTCCAT	105
YUCCA4	LOC_Os01g12490	AGGGCCAGATGATGCACTCC AGGTCGAGGGACACCTCCAT	109
YUCCA5	LOC_Os12g32750	TCTACGCCACCGGATTCACC	101
		GGCGAGGGACTTGGTCCAG
YUCCA6	LOC_Os07g25540	CGCCATGTCTGACCTGTTGC	107
		GGAACCGGAGGAGGAAGACG
YUCCA7	LOC_Os04g03980	CCCAACGGATGGAAGGGTGA	149
		GCCGTGCTCTTCTTGGTTGG

Fig. 2. Temporal patterns of total chlorophyll, MDA, free-IAA and IAA-ASP contents in flag leaves from 0 to 28 days post anthesis between the wild type and the psf mutant.^ A, Chlorophyll contents; B, MDA content; C, Free IAA content; D, IAA-ASP content. Vertical bars represent standard deviation (n = 3). * indicate significant difference (P < 0.05).

Fig. 3. Temporal patterns of the mRNA transcript levels of YUCCAs isogenes in flag leaves from 0 to 28 days post anthesis between the wild type and the psf mutant.^ A, Comparison of seven YUCCAs isoform genes expressions at 0 day after anthesis; B, YUCCA1; C, YUCCA2; D, YUCCA3; E, YUCCA4; F, YUCCA6; G, YUCCA7. Vertical bars represent standard deviation (n = 3). *

Fig. 4. Total chlorophyll contents, MDA accumulaton, free IAA and IAA-ASP contents of the wild type and the psf mutant among three N regimes.^ A, Chlorophyll contents; B, MDA content; C, Free IAA content; D, IAA-ASP content; LN, Low N level (1.45 mmol/L); NN, Normal N level (2.9 mmol/L); HN, High N level (5.8 mmol/L). Values followed by the same letter for each rice genotype within the same sampling stage are not significantly different at the 0.05 level. DAA, Days after anthesis.

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