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赵福成, 景立权, 闫发宝, 陆大雷, 王桂跃, 陆卫平. 灌浆期高温胁迫对甜玉米籽粒糖分积累和蔗糖代谢相关酶活性的影响. 作物学报, 2013, 39(9): 1644-1651[ZHAO Fu-Cheng, JING Li-Quan, YAN Fa-Bao, LU Da-Lei, WANG Gui-Yue, LU Wei-Ping. Effects of Heat Stress During Grain Filling on Sugar Accumulation and Enzyme Activity Associated with Sucrose Metabolism in Sweet Corn. Acta Agronomica Sinica, 2013, 39(9): 1644-1651]  
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灌浆期高温胁迫对甜玉米籽粒糖分积累和蔗糖代谢相关酶活性的影响
赵福成1,2, 景立权1, 闫发宝1, 陆大雷1, 王桂跃2, 陆卫平1,*
1扬州大学江苏省作物遗传生理重点实验室 / 农业部长江中下游作物生理生态与栽培重点开放实验室, 江苏扬州225009
2浙江省东阳玉米研究所, 浙江东阳322100
*通讯作者(Corresponding author): 陆卫平, E-mail:wplu@yzu.edu.cn, Tel: 0514-87979377
基金:本研究由国家自然科学基金项目(30971731, 31000684, 31271640), 江苏高校优势学科建设工程项目和江苏高校优秀科技创新团队、农业科研杰出人才及其创新团队项目资助。
摘要

为明确高温对甜玉米籽粒产量和品质的影响, 以甜玉米厦甜1号和粤甜16为材料, 人工授粉3 d后, 利用人工气候室分别进行昼间高温(HT) 35℃和正常气温(CK)处理, 研究了甜玉米籽粒灌浆过程中粒重、糖分积累和蔗糖代谢相关酶活性的动态变化。结果表明, 与正常气温相比, 高温缩短甜玉米灌浆进程, 显著降低粒重、含水量, 提高皮渣率。在最佳采收期(水分含量为68%~74%)甜玉米鲜百粒重分别下降了20.8% (厦甜1号)和16.4% (粤甜16)。在甜玉米籽粒灌浆过程中可溶性糖和蔗糖的含量随授粉后时间先升高后降低, 高温处理不利于可溶性糖和蔗糖积累, 籽粒中糖分含量降低, 淀粉含量升高。籽粒中蔗糖的合成与分解主要由磷酸蔗糖合成酶(SPS)和蔗糖合成酶(SS)催化, SS催化反应是可逆的。高温明显降低SPS和SS合成方向活性, 提高SS分解方向活性, 导致糖分含量降低, 品质变 劣。高温缩短两品种SS (合成方向)活性峰值出现的时间, 而对于SPS活性峰值出现时间厦甜1号被缩短, 粤甜16 为不变。

关键词: 甜玉米; 高温胁迫; 糖分积累; 蔗糖代谢; 酶活性
Effects of Heat Stress During Grain Filling on Sugar Accumulation and Enzyme Activity Associated with Sucrose Metabolism in Sweet Corn
ZHAO Fu-Cheng1,2, JING Li-Quan1, YAN Fa-Bao1, LU Da-Lei1, WANG Gui-Yue2, LU Wei-Ping1,*
1 Key Laboratory of Crop Genetics and Physiology of Jiangsu Province / Key Laboratory of Crop Physiology, Ecology and Cultivation in Middle and Lower Reaches of Yangtze River of Ministry of Agriculture, Yangzhou University, Yangzhou 225009, China
2 Dongyang Institute of Maize Research, Dongyang 322100, China
Abstract

With the trends of global warming, the extreme high temperature stress often happens during crop grain filling in the world. Heat stress has been an important factor limiting grain yield and quality. To determine the effects of heat stress on fresh kernel yield, quality and enzyme activities of sucrose metabolism, we carried out an experiment in artificial phytotron using two sweet corn cultivars (Xiatian 1 and Yuetian 16) with two typical temperature treatments (high temperature, HT and control, CK) during grain filling. The results indicated that the growth process of sweet corn was accelerated, but the weight and quality of kernel was decreased seriously under high temperature. The weight of 100-fresh-kernel and kernel water content were markedly reduced, but content of pericarp was increased. At the optimum harvest stage of fresh ear (with kernel water content 68%-74%), the fresh kernel weight of the two cultivars was reduced significantly by 20.8% (Xiatian 1) and 16.4% (Yuetian 16) under higher temperature respectively. The contents of soluble sugar and sucrose first increased and then decreased during the grain filling stage. High temperature was not favorable to sugar accumulation, resulting in sucrose content decrease and starch content increase. Sucrose phosphate synthetase (SPS) and sucrose synthetase (SS) play an important role in sucrose synthesis and degradation. SS catalyzes the interconversion of sucrose. Heat stress decreased the activities of SPS and SS (synthetic) and increased the activity of SS (cleavage), which inevitably leads to a depression in sucrose content and a reduction in kernel quality. The maximum SS (synthetic) activity in process of grain filling of two sweet corns appeared earlier under high temperature, while that of SPS activity appeared earlier in Xiatian 1 and did not in Yuetian 16.

Keyword: Sweet corn; Heat stress; Sugar accumulation; Sucrose metabolism; Enzyme activity

甜玉米又称“果蔬玉米”, 是玉米的甜质型亚种, 我国目前种植的主要是受胚乳突变基因 sh2控制的超甜玉米。可溶性糖含量直接决定甜玉米的食用品质, 蔗糖是可溶性糖的主要组成部分[1,2]。蔗糖代谢主要由磷酸蔗糖合成酶(SPS)和蔗糖合成酶(SS)催化, SS催化的反应是可逆的[3,4]。蔗糖代谢相关酶的活性受温度[5,6,7]、光照[8]、水分[9,10]等因素的影响较大, 通过对蔗糖代谢相关酶的调控可提高甜玉米蔗糖含量进而提高甜玉米品质[11]。

随着温室效应的加剧, 全球气候变暖不可逆 转[12], 至2100年大气温度将上升1.4~5.8℃, 全球平均气温上升的同时, 极端性气候如夏季高温等也在许多区域频繁地出现, 且持续时间更长[13,14]。高温是影响玉米产量和品质的主要因素之一, 成为研究的热点。前人在水稻、小麦和普通玉米上进行了大量的研究[15,16,17,18], 结果表明高温胁迫可以加快生育进程, 缩短灌浆时间, 减少干物质积累量, 降低粒重和容重, 从而使产量和品质大幅下降。高温影响普通玉米粒重的原因不在于可溶性糖供应不足, 而在于高温降低了籽粒中淀粉代谢酶特别是ADPG焦磷酸化酶和淀粉合成酶的活性, 使糖分向淀粉的转化受阻, 淀粉合成受影响[19]。

关于高温胁迫对甜玉米的影响研究较少, 主要是通过调整播期或异地栽培来研究温度对甜玉米产量和品质的影响, 由于田间试验涉及的气候因素较多, 很难通过田间试验来揭示单一温度因子对品质的影响, 而高温胁迫对甜玉米糖分积累和蔗糖代谢酶相关活性的研究尚未见报道。我国甜玉米种植主要集中在南方地区, 灌浆结实期异常高温频频出现, 影响籽粒灌浆, 导致产量降低、品质变劣。本文利用人工气候室, 探讨了高温对甜玉米籽粒中糖分积累和蔗糖代谢相关酶活性的影响, 为进一步开展优质栽培和品种选育研究提供理论指导。

1 材料与方法
1.1 试验材料与设计

试验于2012年在扬州大学江苏省作物遗传生理重点实验室盆栽场进行。供试品种为2011年筛选出来的耐热性较强的甜玉米品种粤甜16 (Yuetian 16)和耐热性较弱的品种厦甜1号(Xiatian 1)。试验采用盆栽, 盆直径50 cm, 高55 cm, 盆土含有机质15.8 g kg-1、全氮1.52 g kg-1、速效氮112.6 mg kg-1、速效磷17.9 mg kg-1、速效钾100.2 mg kg-1。每盆基肥施N﹕P2O5﹕K2O含量各为15%的有机肥15 g, 在大喇叭口期追施尿素9 g。3月18日播种, 4月2日移栽于实验盆钵中, 每盆3株, 每个品种50盆, 拔节期留苗2株。于吐丝前选择生育进程一致的果穗挂牌标记, 雌穗套袋, 6月3日对厦甜1号、6月8日对粤甜16人工授粉, 授粉后3 d移入人工气候室。设高温处理(35℃, HT)和对照(自然温度, CK)。前者白天采用电热板加热控温, 晚上关掉加热电源打开门窗, 后者不加热并保持门窗开启, 均自动加湿使湿度在75%左右, 保持除温度不一致外, 光照、湿度等环境条件基本一致。每天用最高最低温度记录温度变化(图1)。

图1 高温处理和对照日最高气温和最低气温变化HT: 高温处理; CK: 对照。HT: high temperature; CK: control.Fig. 1 Changes of daily maximum temperature and daily minimum temperature under heat stress and control conditions

1.2 样品采集

两品种分别在授粉后10、14、18、22、26、30 d 每处理取5个挂牌果穗, 用于各项测定和分析。剥取果穗中部籽粒混匀, 分成6份, 其中一半在105℃烘箱内杀青30 min, 然后在70℃恒温条件下烘干至恒重, 同时测定含水量; 另外一半置-80℃超低温冰箱保存, 用于酶活性测定。

1.3 测定项目与方法

用蒽酮比色法测定可溶性糖和淀粉含量, 用间苯二酚法测定蔗糖含量。

参照刘萍等[20]的方法测定皮渣率。

参照Doehlert等[21]和Ou-Lee等[22]的方法并略作改进提取酶液。称取1.00 g左右冰冻籽粒于研钵中加液氮研磨成粉末再加入10 mL预冷的50 mmol L-1 HEPES-NaOH缓冲液(pH 7.5), 经10 000转 min-1冰冻离心10 min, 上清液即为酶提取液。

参照Wardlaw[23]的方法, 略作改进测定蔗糖酶活性。蔗糖磷酸合成酶(SPS)活性测定步骤如下: 50 μL酶提取液加50 μL HEPES-NaOH、20 μL 50 mmol L-1 MgCl2、20 μL 100 mmol L-1 UDPG、20 μL 6-磷酸果糖于30℃水浴锅中反应30 min, 迅速加入200 μL 2 mol L-1 NaOH摇匀, 沸水浴10 min。再加2.0 mL 30%的盐酸于80℃保温10 min, 最后加1 mL 1%的间苯二酚, 同样在80℃保温10 min后冷却至室温, 加3.64 mL超纯水摇匀, 用722S可见分光光度计于480 nm波长下比色, 用蔗糖生成量表示酶活性。蔗糖合成酶(SS)合成和分解方向的活性测定步骤如下: 50 μL酶提取液加50 μL HEPES-NaOH、20 μL 50 mmol L-1 MgCl2(SS合成)/MgSO4(SS分解)、20 μL 100 mmol L-1 UDPG、20 μL果糖于30℃水浴锅中反应30 min, 迅速加入200 μL 2 mol L-1 NaOH摇匀, 并沸水浴保温10 min。再加2.0 mL 30%的盐酸于 80℃保温10 min, 最后加1 mL 1%的间苯二酚, 在80℃保温10 min后冷却至室温, 加3.64 mL超纯 水摇匀, 用722S可见分光光度计于480 nm波长下比色。

用Microsoft Excel 2007、SPSS 13.0软件处理数据, 采用SigmaPlot 10.0作图。

2 结果与分析
2.1 高温对籽粒百粒鲜重、水分、皮渣率的影响

两品种在不同温度下鲜百粒重的变化随授粉后天数先升高后降低(图2-A, B), 高温处理的最大鲜百粒重出现在授粉后18 d, 对照出现在22 d。高温处理最大鲜百粒重显著低于对照, 厦甜1号比对照低20.8%, 粤甜16比对照低16.4%。两品种鲜食籽粒含水量随授粉后天数变化呈明显下降趋势(图2-C, D), 高温处理均低于对照。在授粉后30 d, 甜玉米籽粒干百粒重显著低于对照, 厦甜1号比对照低28.2%, 粤甜16比对照低20.5%。甜玉米籽粒的皮渣率随授粉后天数逐渐升高(图2-E, F), 两品种在不同温度下表现不一致, 厦甜1号皮渣率在灌浆前期高温处理低于对照, 在灌浆后期高于对照, 粤甜16在整个灌浆期皮渣率均为高温处理高于对照。

2.2 高温对可溶性糖、蔗糖和淀粉的影响

可溶性糖(图3-A, B)和蔗糖(图3-C, D)的含量均随授粉后时间变化先上升后降低, 呈单峰曲线; 随着粒重的增加表现明显的“稀释效应”, 因此粒重增加导致可溶性糖和蔗糖的含量降低。厦甜1号可溶性糖和蔗糖含量峰值高温处理出现在授粉后14 d, 对照出现在22 d; 粤甜16可溶性糖和蔗糖峰值在不同温度下均出现在授粉后18 d。甜玉米一般在授粉后22 d采收, 此时厦甜1号高温处理可溶性糖下降30.3%, 蔗糖下降30.7%; 粤甜16高温处理可溶性糖下降18.3%, 蔗糖下降32.1%。两品种籽粒淀粉含量呈上升趋势(图3-E, F), 在灌浆前、中期淀粉积累量高温处理高于对照, 灌浆后期低于对照。

2.3 高温对蔗糖代谢相关酶活性的影响

SPS活性的高低反应甜玉米光合产物转化为蔗糖的能力。由图4-A, B可以看出, 两品种籽粒SPS活性变化与蔗糖含量变化的趋势基本一致。在籽粒发育过程中, 高温对两品种的影响并不一致, 厦甜1号在灌浆前期, 高温处理下SPS活性高于对照, 在灌浆后期低于对照, SPS活性峰值比对照降低29.5%; 粤甜16在整个灌浆期SPS活性高温均低于对照, SPS活性峰值高温处理比对照降低25.1%。SS有两个作用方向, 催化的反应是可逆的, 可以催化蔗糖的合成和分解。甜玉米籽粒发育过程中SS合成(图4-C, D)活性变化亦为单峰曲线, 两品种SS合成活性高温处理均低于对照, 高温处理峰值出现在授粉后18 d, 对照出现在授粉后22 d。在灌浆前期SS分解(图4-E, F)活性增加缓慢, 在灌浆中后期增加(降低)迅速。随着授粉后天数增加两品种高温处理SS分解活性先升高后降低, 呈单峰曲线, 而对照不断升高。

3 讨论

灌浆期是作物产量和品质形成的关键时期, 玉米灌浆期间最适日平均温度为22~24℃, 温度在23~31℃范围内对籽粒发育影响较小, 高于35℃则会严重影响籽粒的发育[24], 在灌浆初期高温主要是减少胚乳细胞数量使粒重减少, 在灌浆后期高温显著降低植物的光合作用[25], 损害淀粉的合成[26]。Wilhelm等[27]研究发现, 灌浆结实期高温降低了籽粒中蛋白质、淀粉和脂肪的含量。Muchow[28]利用不同的播期处理, 在大田环境下研究了高温对玉米生长发育和最终产量的影响, 发现高温使玉米生长加快, 有效灌浆期缩短, 产量降低。甜玉米适宜采收期籽粒含水率在68%~74%[29], 本研究中常温下两个甜玉米品种在授粉后22 d适宜采收, 而高温处理则授粉后18 d适宜采收。高温缩短了甜玉米生育期, 降低了粒重、可溶性糖和蔗糖含量, 从而使产量和品质下降, 这和前人在水稻、普通玉米上的研究结果一致。玉米对高温胁迫存在基因型差异, 高温处理最大鲜百粒重厦甜1号比对照低20.8%, 粤甜16比对照低16.4%。厦甜1号在灌浆前期高温处理皮渣率低于对照, 在灌浆中后期高于对照, 粤甜16在整个灌浆期皮渣率均为高温处理高于对照。可溶性糖含量是评价甜玉米品质优劣的主要指标, 蔗糖是可溶性糖的主要组分。高温胁迫下厦甜1号可溶性糖和蔗糖峰值出现在授粉后14 d, 对照出现在授粉后22 d, 而粤甜16不同温度处理下均出现在授粉后18 d。在适宜采收期, 可溶性糖含量高温处理(授粉后18 d)比常温对照(授粉后22 d)厦甜1号下降了18.3%, 粤甜16仅下降了3.3%。从最佳采收期的籽粒产量和可溶性糖含量来看, 粤甜16的降幅更小, 说明粤甜16对高温的承受能力比厦甜1号强。

图2 授粉后高温胁迫下甜玉米鲜百粒重、籽粒含水量和皮渣率的动态变化HT: 高温处理; CK: 对照。HT: high temperature; CK: control.Fig. 2 Dynamics of the 100-fresh-kernel weight, water content and pericarp and dregs content in grains of sweet corn under heat stress after pollination

SPS是以UDPG为供体, 以6-磷酸果糖(F-6-P)为受体的蔗糖合成调节关键酶, 合成磷酸蔗糖, 进而在磷酸蔗糖酯酶的作用下脱磷酸形成蔗糖[3]。SS存在于细胞质中, 催化的反应是可逆的, 当SS分解方向起作用时, 分解蔗糖生成UDPG和果糖, SS合成方向有利于蔗糖的形成[30]。本研究中, 甜玉米蔗糖的合成和降解动态平衡受SPS和SS共同作用, 灌浆前期SPS、SS合成和SS分解方向活性均呈上升趋势, SPS和SS合成活性升高的比SS分解方向快, 籽粒内蔗糖的合成大于分解, 导致糖分积累; 灌浆后期, SPS和SS合成方向活性下降, 而SS分解活性升高, 籽粒内蔗糖的合成小于分解, 导致糖分含量降低, 淀粉含量升高, 这和刘鹏等[30]、曹玉军等[31]在甜玉米上的研究结果一致。

图3 授粉后高温胁迫下甜玉米籽粒可溶性糖、蔗糖和淀粉含量的动态HT: 高温处理; CK: 对照。HT: high temperature; CK: control.Fig. 3 Dynamics of the contents of soluble sugar, sucrose, and starch in grains of sweet corn under heat stress after pollination

酶活性受温度影响很大, 籽粒中蔗糖代谢相关酶的活性对高温的响应必将影响糖分积累, 但高温对蔗糖代谢酶的影响不尽相同。Ebrahim等[32]研究指出高温降低蔗糖代谢酶的活性, 从而降低蔗糖和淀粉的含量, Lafta等[33]研究认为高温提高SPS活性。本研究表明温度对SPS (图4-A, B)的影响在2个甜玉米中表现不一致, 厦甜1号灌浆前期高温胁迫提高籽粒中SPS活性, 在灌浆中后期降低SPS活性, 粤甜16整个灌浆期高温都降低SPS活性, SPS活性峰值高温处理分别降低29.5% (厦甜1号)和25.1% (粤甜16)。前人研究认为SS主要起蔗糖分解作用, 将叶片等源器官合成的蔗糖运输到籽粒后再将其降解, 以供淀粉合成用, 高温下SS分解活性下降, 抑制淀粉的合成[34]。本研究发现两个品种高温均降低SS合成方向(图4-C, D)的活性, 在灌浆前期提高SS分解方向的活性, 而灌浆末期SS分解活性急剧下降, 这可能是胚乳隐性基因的突变造成的, 甜玉米胚乳隐性基因突变发生在淀粉合成的上游, 淀粉合成受阻, 糖分大量积累。高温下由于SS分解方向活性升高, 蔗糖转化成淀粉的能力提高导致甜玉米籽粒中糖分含量下降, 淀粉含量升高; 在灌浆末期(授粉30 d后)高温处理的甜玉米叶片开始枯萎, 光合能力下降, 光合产物供应不足以及籽粒含水量下降导致SS分解方向的活性下降, 淀粉合成能力也降低, 淀粉含量下降。

图4 授粉后高温胁迫下甜玉米籽粒SPS、SS (合成方向)、SS (分解方向)活性的动态变化HT: 高温处理; CK: 对照。HT: high temperature; CK: control.Fig. 4 Dynamics of the activities of SPS, SS (synthetic), and SS (cleavage) in grains of sweet corn under heat stress after pollination

4 结论

高温缩短了甜玉米达到最佳采收期(水分含量在68%~74%)所需天数, 降低了鲜籽粒的产量及可溶性糖和蔗糖含量。高温降低了起蔗糖合成作用的酶(SPS和SS合成方向)活性, 提高了分解蔗糖的酶(SS分解方向)活性。该影响存在基因型差异, 耐热性较强的品种粤甜16籽粒鲜重和可溶性糖的含量下降幅度比耐热性较弱的品种厦甜1号小。高温缩短两品种SS (合成方向)活性峰值出现的时间, 而对SPS活性峰值出现时间厦甜1号被缩短粤甜16为不变。高温对不同品种籽粒蔗糖代谢酶活性的影响不一致, 其机制尚需进一步研究。在生产实践中可以采用春季提早或夏季推迟播期来避开高温或选择 耐热品种等措施来减轻高温对甜玉米产量和品质的影响。

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