Hormones in the grains in relation to sink strength and postanthesis development of spikelets in rice

Inferior spikelets usually exhibit a slower grain filling rate and lower grain weight than superior spikelets in a rice (Oryza sativa L.) panicle. This study investigated whether the variations in grain filling between the two kinds of spikelets were attributed to their sink strength and whether the sink strength was regulated by the hormonal levels in the grains. Using two field-grown rice genotypes, the division rate of endosperm cells, hormonal levels in the grains, and grain weight of both superior and inferior spikelets were determined during the grain filling period. The results showed that superior spikelets had dominance over inferior spikelets in endosperm cell division rate and cell number, grain filling and grain weight. Changes in zeatin (Z) and zeatin riboside (ZR) contents paralleled and were very significantly correlated with the cell division rate and cell number. Cell division rate and the content of indole-3-acetic acid (IAA) in the grains were also significantly correlated. Gibberellin (GAs; GA₁+ GA₄) content of the grains was high but ABA levels were low at the early grain filling stage. ABA increased substantially during the linear phase of grain growth and was very significantly correlated with grain dry weight during this period. Application of kinetin at 2 through 6 days post anthesis (DPA) significantly increased cell number, while spraying ABA at 11 through 15 DPA significantly increased the grain filling rate. The results suggest that differences in sink strength are responsible for variations in grain filling between superior and inferior spikelets. Both cytokinins and IAA in the grains may mediate cell division in rice endosperm at early grain filling stages, and therefore regulate the sink size of the grain, whereas ABA content correlates with sink activity during the linear period of grain growth.     

氮素形态对小麦花后不同器官内源激素含量的影响

采用盆栽方法,研究了酰胺态氮、铵态氮和硝态氮对小麦(Triticum aestivum)花后根系、旗叶和籽粒内源激素IAA、GA₃、ABA和ZR含量的影响。结果表明,小麦不同器官的内源激素含量对3种氮素形态的响应不同。氮素形态调节籽粒灌浆是通过根系、旗叶和籽粒中内源激素的协同作用而实现的。酰胺态氮与硝态氮处理相比,小麦花后5~15 d,旗叶GA₃含量、籽粒IAA和ABA含量较高,籽粒灌浆速率(Grain-filling rate, GFR)较高;花后15~25 d,根系GA₃含量、旗叶IAA和GA₃含量、籽粒ABA含量较高,籽粒IAA含量较低,GFR较低。铵态氮与硝态氮处理相比,小麦花后5 d,籽粒ZR含量较高;花后15 d前后,籽粒IAA、ABA含量较低,GFR较低;花后20~25 d,根系ZR、GA₃含量较低,旗叶IAA、GA₃含量较低,ABA含量较高,籽粒ABA、GA₃含量较低,IAA含量较高,GFR较高。铵态氮比硝态氮处理的小麦籽粒粒重显著增加。铵态氮和酰胺态氮处理比硝态氮处理增产显著。建议在‘豫麦49’施肥时,使用铵态氮或酰胺态氮并配施硝化抑制剂。     

中国沙棘克隆生长对灌水强度的响应规律及其激素调控机制

关于中国沙棘克隆生长调节研究目前局限于外在机制,旨在探讨其克隆生长对灌水强度的响应规律及其激素调控的内在机制。结果表明:随着灌水强度的增大,分株生长、克隆繁殖、克隆扩散能力先升后降,IAA(吲哚-3-乙酸)、ZR(玉米素核苷)、GA_3(赤霉酸)含量及其与ABA(脱落酸)的比值先升后降而ABA含量先降后升。同时,分株生长、克隆繁殖、克隆扩散能力与IAA、ZR、GA_3含量以及IAA/ABA、ZR/ABA、GA_3/ABA呈极显著或显著正相关,与ABA含量呈极显著负相关。灌水强度过小或过大,IAA、ZR、GA_3含量以及IAA/ABA、ZR/ABA、GA_3/ABA低而ABA含量高,克隆生长潜力受到抑制,种群以分株小、数量少(分布稀疏)、扩散(水平根延伸和分枝)能力弱为特征,克隆生长格局倾向于"游击型"、种群早衰概率高;灌水强度适宜,IAA、ZR、GA_3含量以及IAA/ABA、ZR/ABA、GA_3/ABA高而ABA含量低,克隆生长潜力得以充分发挥,种群以分株大、数量多(分布密集)、扩散能力强为特征,克隆生长格局倾向于"聚集型"、种群稳定性高。随着灌水强度过小-适宜-过大的连续变化,中国沙棘通过改变激素状况调控克隆生长,从而形成与灌水强度相适应的克隆生长格局连续体"游击型-聚集型-游击型",种群稳定性呈"低-高-低"的连续变化过程。由此可见:灌水强度诱导内源激素发生改变,激素特征调控克隆生长格局,克隆生长格局决定种群稳定性。     

The effect of plant growth regulator treatments on the levels of ethylene emanating from excised turgid and wilted wheat leaves

Abscisic acid (ABA) inhibits the production of ethylene induced by water stress in excised wheat leaves and counteracts the stimulatory effect of 6-benzyladenine (BA) on this process. The stimulatory effect of BA and the inhibitory effect of ABA were equally pronounced whether external or endogenous ethylene levels were determined. When leaves were sprayed or floated on solutions of BA, indole-3-acetic acid (IAA), gibberellic acid (GA₃), or ABA, the relative activities of these growth regulators on stress-induced ethylene at 10^-4 mol l^-1 were BA>IAA >GA₃>controls>ABA. In non-stressed leaves, however, where the levels of ethylene produced were 2–20 times smaller, the relative activities were IAA >BA>GA₃>controls>ABA. The effects of BA and ABA spray treatment on water stress induced ethylene were closely similar whether the solutions were applied 2 or 18 h prior to the initiation of water stress. The relationships between the levels of endogenous growth regulators in the plant and ethylene release induced by water stress are discussed.Abbreviations BA 6-benzyladenine - IAA indole-3-acetic acid - GA₃ gibberellic acid - ABA abscisic acid - GLC gas-liquid chromatography - _leaf leaf water potential     

外源GA3对紫斑牡丹幼苗叶片解剖结构与光合特性及内源激素含量的影响

以1年生紫斑牡丹幼苗为试验材料,采用不同浓度(0、100、300、500 mg/L)赤霉素(GA_3)喷施叶片处理,通过透射电镜、扫描电镜、光学显微镜观察幼苗叶片解剖结构,光合仪测定幼苗光合参数并以酶联免疫吸附法测叶片内源激素含量,探究外源GA_3对紫斑牡丹幼苗叶片解剖结构、光合特性和内源激素水平的影响。结果表明:(1)低浓度GA_3处理的紫斑牡丹叶肉细胞增大,栅栏组织外层细胞中叶绿体数量增加,高浓度GA_3处理则与之相反;GA_3处理叶片的栅栏组织/海绵组织比值(P/S)、组织结构紧密度(CTR)均下降,而其组织结构疏松度(SR)增加;GA_3处理的幼苗叶片的叶肉细胞内各叶绿体大小显著大于对照,随着GA_3处理浓度增加,紫斑牡丹叶肉细胞内叶绿体的体积趋于增大,类囊体垛叠凝聚逐渐松散,叶绿体上淀粉颗粒在300 mg/L GA_3处理中较明显;叶片气孔长度、宽度、气孔器大小、气孔开度和气孔密度随着GA_3浓度升高先升高后下降,同时叶片上表皮角质层厚度随GA_3浓度的升高而增加。(2)紫斑牡丹叶片净光合速率(P_n)、气孔导度(Cond)、蒸腾速率(T_r)、水分利用率(WUE)在100和300 mg/L GA_3处理下大都显著高于对照,且300 mg/L GA_3处理显著高于其余处理,而其在500 mg/L GA_3处理下显著低于对照。(3)紫斑牡丹叶片脱落酸(ABA)和吲哚乙酸(IAA)含量均在500 mg/L GA_3下显著高于对照,而在其余浓度处理下不同程度低于对照,叶片内源玉米素核苷(ZR)和GA_3含量均在300 mg/L GA_3处理下显著高于其余处理和对照,而其余处理相比对照均无显著变化;叶片的ZR/ABA、ZR/IAA、ZR/GA_3和(IAA+GA_3+ZR)/ABA比值都在300 mg/L GA_3处理下显著高于其他处理,叶片的IAA/ABA和ABA/GA_3比值均在500 mg/L GA_3处理下显著高于其他处理。研究发现,适宜浓度外源GA_3处理,能显著提高紫斑牡丹幼苗叶片光合速率、水分利用效率及蒸腾速率,调节植物体内源激素的含量及平衡,从而使叶片能合成较多有机物,促进幼苗生长。     

Effects of exogenous ABA and cytokinin on leaf photosynthesis and grain protein accumulation in wheat ears cultured <Emphasis Type="Italic">in vitro</Emphasis>

A detached culture system and steady-state ¹⁵N labeling technique were used to study the effects of exogenous ABA and ZR on photosynthetic characteristics, nitrogen remobilization and the activities of key enzymes for nitrogen metabolism in detached wheat parts during grain protein accumulation. The differences in net photosynthetic rate, chlorophyll content (SPAD value) and soluble protein content in the flag leaves of detached culture system between the treatments of ABA and ZR showed that ABA facilitates the post-anthesis senescence course compared to the ZR treatment. The differences in the changes of ¹⁵N amount in different organs in the detached culture system between the ABA and ZR treatments showed that nitrogen remobilization from vegetative organs to the grain is accelerated by the ABA treatment but is delayed by ZR. The activities of GS and GPT in grains treated with ABA were significantly higher than those with the control treatment at 5 DAC, but reduced significantly compared with control at 11 DAC. The two enzyme activities in grains were reduced significantly by ZR at 5 DAC and increased significantly at 11 DAC, compared with those treated with ABA. The above changes of enzyme activity showed that the ABA treatment hastens amino acid conversion into grains and protein accumulation in grains, whereas the ZR treatment delays these processes. A significant reduction in grain weight with ABA treatment is associated with the reduction of net photosynthesis, chlorophyll content, and soluble protein content in flag leaves. Compared with the control and ZR treatments, a significant increase in grain protein content with the ABA treatment may result from the accelerating effects of ABA on N remobilization, amino acid conversion into grains and protein accumulation in grains.     

Hormones in the grains and roots in relation to post-anthesis development of inferior and superior spikelets in japonica/indica hybrid rice

Grain filling is usually not adequate in later-flowering inferior spikelets in japonica/indica (J/I) hybrid rice (Oryza sativa) although it shows stronger hybrid vigor than indica/indica (I/I) hybrid. This study investigated the potential causes by examining changes in zeatin (Z) + zeatin riboside (ZR), indole-3-acetic acid (IAA), gibberellins (GAs, GA₁ + GA₄), and abscisic acid (ABA) in spikelets and roots during the grain filling period. The inferior spikelets of J/I hybrid exhibited low rate of endosperm cell division and slow grain filling. During the early grain filing period, they had less Z + ZR, IAA, and ABA, but more GAs, than the earlier-flowering superior spikelets. If compared to the inferior spikelets of the I/I hybrid, the J/I inferior spikelets also had less Z + ZR, IAA, and ABA. Rates of endosperm cell division and grain filling were positively and significantly correlated with Z + ZR and ABA contents in both grains and roots or IAA in grains, whereas not significantly correlated with GAs either in grains or roots or IAA in roots. Applications of kinetin, IAA, or ABA to spikelets, or kinetin and ABA to roots, enhanced cell division and grain filling in the inferior spikelets. Results suggest that low contents of cytokinins and ABA in both grains and roots and low contents of IAA in grains may result in the poor filling of inferior spikelets in the J/I hybrid.     

花后土壤水分状况对小麦籽粒淀粉和蛋白质积累关键调控酶活性的影响

在温室盆栽条件下,以2个不同蛋白质含量的冬小麦(Triticum aestivum L．)品种皖麦38和扬麦9为材料,研究了花后第4天开始的土壤干旱(SRWC=45％～50％)和渍水对籽粒蛋白质和淀粉积累关键调控酶活性的影响。小麦叶片和籽粒的测定结果均表明,小麦源库器官中籽粒蛋白质和淀粉积累的关键调控酶活性变化趋势在2个品种间基本一致。与对照(SRWC=75％～80％)相比,干旱和渍水均明显降低了花后旗叶中蔗糖含量和磷酸蔗糖合成酶(SPS)活性,而氨基酸含量和谷氨酰胺合成酶(GS)活性略有下降。干旱和渍水均降低了籽粒库蔗糖合成酶(SS)和结合态淀粉合成酶(GBSS)活性,可溶性淀粉合成酶(SSS)活性降低尤甚。其中干旱处理下SS的下降比渍水更为明显。与对照相比,渍水明显降低了籽粒谷丙转氨酶(GPT)和GS活性,而干旱的影响较小。相关性分析结果表明籽粒淀粉产量和含量与SPS,SSS和GBSS活性的关系比与SS活性的关系更为密切,籽粒蛋白质产量和含量与叶中GS和籽粒中GPT活性的关系比与籽粒中GS关系活性更为密切。这些结果表明小麦源库器官中调控籽粒蛋白质和淀粉积累的关键酶活性变化是花后不同水分状况影响籽粒淀粉和蛋白质特性的重要因素。     

水稻籽粒激素对产量和品质的调控效应研究进展

水稻籽粒激素含量甚微,却能有效调控产量与品质的形成。该文主要对近年来国内外有关水稻籽粒中激素(IAA、GA1+4、Z、ZR、iPA、ABA、ETH)含量在不同环境下的变化规律、各激素及其互作对水稻籽粒产量和品质性状的调控效应和调控机理进行综述,并讨论了该领域未来的研究重点和方向,为今后相关研究提供信息参考。     

兰州百合鳞茎发育及低温解除休眠过程中内源激素的变化

以兰州百合为试材,研究了鳞茎发育过程中以及2、6、10℃条件下保湿贮藏101 d内母鳞茎与新鳞茎中内源激素的变化。结果表明：鳞茎发育过程中内源ABA含量以及母鳞茎的GA₃与ZR含量增加,而内源IAA含量以及新鳞茎的GA₃与ZR含量下降。低温贮藏期间,母鳞茎与新鳞茎的GA₃、IAA含量均有升高过程,而ABA含量呈下降趋势;新鳞茎的ZR含量呈下降趋势,母鳞茎的ZR含量也有升高过程。低温处理初期的34 d内,内源激素变化最为显著。不同贮藏温度相比较,ABA含量差异不大,GA₃含量随温度升高而下降。在富含淀粉的新鳞茎中,GA₃和ABA表现出极显著的负相关关系,而在淀粉含量较低的母鳞茎中GA₃和ABA无相关性。通径分析结果表明,母鳞茎与新鳞茎的物质代谢机制不同,母鳞茎的物质变化受内源GA₃的调控,新鳞茎主要是ABA作用的结果。     

水培条件下不同磷水平对毛竹实生苗生长发育的影响

以毛竹(Phyllostachys edulis)实生苗为材料,采用Hoagland营养液水培方法,研究不同磷浓度下毛竹生长、根系发育、激素含量等的差异。结果表明:磷浓度较低时,可以促进毛竹实生苗根系长度及根系总表面积的增长。随着磷浓度的增加,实生苗生物量干重及根冠比呈先上升后下降趋势,磷浓度为1 mmol L-1时达到最大。无磷处理时,根中的IAA、ZR、GA3和ABA等4种内源激素含量随着处理时间的延长均先升高再降低;其他浓度磷处理根中IAA、ZR和GA3(0.5 mmol L-1磷除外)含量随着处理时间的延长大致呈先降低后升高的趋势,而ABA(0.5 mmol L-1磷除外)含量随着处理时间的延长变化不明显。不同浓度磷处理,叶片中IAA、GA3和ABA含量总体上呈下降趋势,ZR含量总体上呈上升趋势。以上结果表明不同浓度的磷处理对毛竹内源激素含量的变化有显著的影响,而内源激素含量变化与毛竹实生苗根系变化密切相关。     

Effects of exogenous hormones on floret development and grain setin wheat

At specific stages during floret development, solutions of IAA,GA₃, zeatin and ABA were injected into the leaf sheath around theyoung spike of wheat (Triticum aestivum L.) to study theregulating effects of exogenous hormones on floret development. Zeatin promotedfloret development and significantly increased the number of fertile florets aswell as grain set, especially at the stage of anther-lobe formation. Zeatinalsoincreased the sugar concentrations in spikes at anthesis. In contrast, IAA,GA₃ and ABA inhibited floret development, with different patternsforeach of the hormones. IAA inhibited the development of the whole spike and allflorets in the spikelets such that grain loss occurred in all positions in thespikelets. GA₃ increased the number of fertile florets per spike,butdecreased grain set of the third floret in each spikelet, especially whenapplied at terminal spikelet formation. ABA inhibited floret development, anddecreased the number of fertile florets and grain set at almost all developmentstages, except at anther-lobe formation. The inhibitory effect of ABA wasmainlyon the first and third florets in each spikelet.     

Germination and <Emphasis Type="Italic">In Vitro</Emphasis> Growth of Petunia Male Gametophyte Are Affected by Exogenous Hormones and Involve the Changes in the Endogenous Hormone Level

The data obtained characterize the changes in the contents of endogenous phytohormones (IAA, cytokinins, GA, and ABA) in germinating pollen grains and growing pollen tubes of a self-compatible clone of petunia (sPetunia hybrida L.) within an 8-h period under in vitro conditions. The hydration and initiation of germination of pollen grains brought the ABA content down to a zero level, while the levels of GA, IAA, and cytokinins increased 1.5–2-fold. Later, in the growing pollen tubes, the GA content increased twofold, while the levels of IAA and cytokinins decreased. The exogenous ABA and GA₃ considerably promoted pollen germination and pollen tube growth; however, only the treatment with GA₃ produced the maximum length of pollen tubes. The exogenous IAA promoted and the exogenous cytokinins hindered the growth of pollen tubes. The membrane potential, as assessed with a potential-sensitive dye diS-C₃-(5), considerably increased in the pollen grains treated with ABA and benzyladenine, whereas IAA and GA₃ did not practically affect it. The authors conclude that the mature pollen grains contain the complete set of hormones essential for pollen germination and pollen tube growth. ABA, GA, and IAA together with cytokinins control the processes of pollen grain hydration, germination, and pollen tube growth, respectively.__________Translated from Fiziologiya Rastenii, Vol. 52, No. 4, 2005, pp. 584–590.Original Russian Text Copyright © 2005 by Kovaleva, Zakharova, Minkina, Timofeeva, Andreev.     

不同成花量金花茶花果期果枝叶内源激素的变化

该研究采用ISSR分子标记,对黄枝油杉7个自然种群的遗传多样性进行了分析。结果表明：用12条ISSR引物对218个黄枝油杉个体进行扩增,共扩增出125个位点。在物种水平上,多态性位点百分数( PPL)为100.00％,Shannon信息多样性指数( I)为0.4177,Nei’ s基因多样性指数( H)为0.2666;在种群水平上,多态性位点百分数(PPL)在71.20％~92.00％之间,平均值为80.69％,Shannon信息多样性指数(I)在0.3273~0.3886之间,平均值为0.3548,Nei’ s基因多样性指数( H)在0.2139~0.2478之间,平均值为0.2291。这说明黄枝油杉在物种水平和种群水平上均显示出较高的遗传多样性。 Nei’ s遗传多样性分析( Gst＝0.1433)和AMOVA分析(Φst＝17.91％)表明,黄枝油杉的遗传变异主要存在于种群内,种群间的遗传分化程度较低,种群间保持一定的基因交流( Nm＝2.9890>1)。 Mantel分析显示,黄枝油杉种群间的遗传距离和地理距离之间不存在显著的相关关系( r＝0.4567, P＝0.0610>0.05)。     

Interactive effects of α-NAA and UV-B radiation on the endogenous hormone contents and growth of Trichosanthes kirilowii Maxim seedlings

The impact of UV-B radiation on endogenous hormones in plants has recently drawn attention from researchers. The mechanism for reduced stem elongation by UV-B might be due to changes in the phytohormone levels, especially IAA, which plays a role in stem elongation. In this study, effects of UV-B radiation on Trichosanthes kirilowii Maxim (T. kirilowii) seedlings in greenhouse-grown plants were investigated. The results indicated that: (1) In comparison to controls, exposure to 0.029 Jm^?2 s^?1. UV-B radiation led to accumulation of endogenous abscisic acid (ABA) and zeatinriboside (ZR) in the plant contents, and decreased contents of endogenous indole-3-acetic acid (IAA) and gibberellic acid (GA_1/3). Exposure to UV-B radiation reduced the height and leaf area of plants. As a result, total biomass (plant dry weight) was lower. (2) In comparison to controls, addition of 2 mg l^?1 α-naphthaleneacetic acid (α-NAA) slightly increased the contents of IAA, GA_1/3 and ZR, and decreased the content of ABA in leaves. This addition of α-NAA significantly increased plant height and leaf area, but only slightly increased total biomass. (3) Addition of α-NAA to UV-B-exposed plants: increased the content of endogenous IAA, GA_1/3 and ZR; decreased accumulation of endogenous ABA; and increased plant height and leaf area in comparison to plants that only were exposed to UV-B. Moreover, total biomass increased slightly. This suggests that addition of α-NAA may compensate to a certain extent for the lack of IAA resulting from UV-B radiation; it also increases the content of GA_1/3 and ZR, decreases the accumulation of ABA, and promotes the growth of plants.     

外源赤霉素对紫斑牡丹种子萌发的影响

以紫斑牡丹种子为试验材料,研究不同浓度的赤霉素(GA_3)处理对种子生根以及生根过程中营养物质、酶活性和内源激素水平变化的影响,为探讨紫斑牡丹种子萌发机制提供依据。结果表明:(1)GA_3处理能够促进种子生根,并以300 mg/L GA_3处理对种子生根效果最好,与对照相比可提前14.67 d生根,生根率可达71.00%。(2)与对照相比,GA_3处理可以在0～15 d时促进种子淀粉水解和可溶性糖的积累,并加速可溶性蛋白的消耗,在0～30 d促进过氧化物酶(POD)活性的提高,从而促进种子萌发生根。(3)在种子沙藏生根过程中,种子脱落酸(ABA)含量呈下降趋势,赤霉素(GA)、玉米素核苷(ZR)和吲哚乙酸(IAA)含量均表现出先上升后下降的趋势,与对照相比,GA_3处理可使种子GA、ZR和IAA的含量在沙藏前期明显上升,以解除种子休眠。研究发现,外源GA_3处理可以调控紫斑牡丹种子内源激素含量和POD活性的变化,促进营养物质转化,从而提前解除种子休眠使其萌发。     

沙生柽柳扦插生根过程插穗相关理化特征分析

选取沙生柽柳半木质化枝条进行苗床扦插,通过实验测定插穗生根过程中内源激素(IAA、GA3、ZR、ABA)含量、可溶性营养物质(糖、蛋白质)含量及相关氧化酶(PPO、POD、SOD、IAAO)活性的动态变化特征,探讨沙生柽柳插穗扦插生根机理。结果表明:(1)沙生柽柳插穗内源激素含量随生根进程而发生变化,其中,IAA含量在扦插35d最大,并出现较大的波动变化;ZR含量在扦插55d前后变化明显,呈现低水平向高水平转化趋势;ABA、GA3含量依次呈先升高后降低再升高的变化过程,并在扦插15d和55d(80d)呈现变化的峰值和谷值。(2)沙生柽柳扦插生根与相关氧化酶活性密切相关,其中,POD、IAAO活性在插穗扦插35d后长时间保持较高水平,直至插穗生根后POD活性明显降低,IAAO活性有所增加;PPO、SOD活性则在插穗扦插15d保持较高活性,且PPO活性的变化均匀,SOD活性的高低交替变化明显。(3)在沙生柽柳扦插生根期间,插穗可溶性糖含量呈现生根前消耗减少与生根后积累增加两大变化过程,可溶性蛋白质含量表现为扦插后逐步积累增加的变化趋势。研究表明,高水平的IAA、ZR和低水平的GA3、ABA共同调控着沙生柽柳插穗生根;IAA能够通过促进插穗POD、PPO、IAAO活性变化来影响生根,较高的POD、IAAO活性可调节插穗IAA水平,高水平的PPO活性则催化插穗IAA-酚酸复合物的形成,进而诱导插穗生根。     

枣花芽分化过程中营养物质和内源激素含量及抗氧化酶活性变化研究

以新疆主栽品种灰枣和骏枣的花芽为材料,测定不同分化时期花芽的可溶性糖、还原糖、淀粉、可溶性蛋白含量,SOD、POD、PPO、CAT活性以及内源GA3、IAA、ABA、ZT水平的变化,并分析它们与花芽分化的关系,为枣花芽分化调控提供理论参考.结果表明:(1)灰枣和骏枣花芽可溶性糖、还原糖和淀粉含量在花芽分化过程的变化趋势...     

Environmental and hormonal regulation of seed dormancy and germination in Cape fynbos Leucospermum R.Br. (Proteaceae) species

The endogenous levels of abscisic acid (ABA), cytokinins (CKs) and gibberellins (GA₁/GA₃ combined) in Leucospermum glabrum embryos were monitored in axes and cotyledons separately during normal germination. Plant growth substance changes were correlated with known morphological, structural and ultrastructural events in the embryo of Proteaceae. The effect of exogenous application of 6-benzyladenine (BA) and GA₄₊₇ under three known dormancy-enforcing environmental conditions were studied in L. glabrum and L. cordifolium. The endogenous levels of the hormone classes GAs and CKs changed phasically during normal germination under a single alternating temperature regime. GA₁/GA₃ levels increased in cotyledons within 3 d of hydration while at the same time initial CK levels decreased. Following this transient peak GAs fell to a low level throughout the germinative period. Subsequently the CKs, Z and ZR, and to a lesser extent their dihydro-derivatives, appeared in both the axes and the cotyledons as fluctuating, transient peaks. Early increases in GAs are thought to control the induction of the germination process. The CK pattern suggests that CKs control at least three major processes of germination sensu stricto following induction: 1) early mobilization of protein and lipid reserves in the axis and later in cotyledons, 2) cotyledon expansion which causes the endotesta to split permitting radicle protrusion and 3) later, radicle growth.Our results indicate that dormancy in intact Leucospermum seeds is enforced by embryo anoxia, regulated by the impermeable exotesta. In addition synthesis of or tissue sensitizing to both hormone classes GAs and CKs depends on moderately low temperature as the primary environmental requirement. For GA synthesis a secondary, daily pulse of high temperature is required. Inhibitory hormones, specifically ABA, appear not to play a role.Abbreviations ABA Abscisic acid - BA 6-benzyladenine - CK Cytokinin - DHZ Dihydrozeatin - DHZR Dihydrozeatin riboside - GA Gibberellin - HPLC High performance liquid chromatography - iP Isopentenyladenine - IPA Isopentenyladenosine - PGS Plant growth substance - RIA Radioimmunoassay - Z Zeatin - ZR Zeatin riboside     

Dynamic changes in carbohydrate metabolism and endogenous hormones during <Emphasis Type="Italic">Tulipa edulis</Emphasis> stolon development into a new bulb

The stolon is the main asexual reproductive organ of Tulipa edulis (Miq.) Baker. It has a special morphology and can develop into a new bulb for propagation. In the current greenhouse experiment, the dynamic changes in carbohydrates and related enzymes, protein and endogenous hormones during T. edulis stolon development were investigated. The results showed that soluble sugar levels were basically declining, whereas starch and protein content rose continuously during stolon development. The adenosine diphosphoglucose pyrophosphorylase (AGPase) activity peaked in the initial swelling stage and stayed a relative high level in the middle swelling stage; sucrose synthase (SS), soluble starch synthase (SSS) and granule-bound starch synthase (GBSS) activities followed the same law that showed rising trends during stolon development. SS activity was significantly inversely related to sucrose content but had significantly positive relations with starch content, SSS and GBSS activities. Gibberellin (GA), indole-3-acetic acid (IAA) and zeatin riboside (ZR) peaked in the initial swelling stage and maintained high levels in the middle swelling stage; they then decreased significantly in the later swelling stage. A substantial increase was observed in abscisic acid (ABA) content until the middle swelling stage, followed by a significant reduction in the later swelling stage. The ratios of ABA to IAA, GA and ZR reached their lowest levels in the initial swelling stage. In conclusion, T. edulis stolon development is a process of new bulb morphogenesis along with the starch accumulation catalyzed by AGPase, SSS and GBSS, using the product of sucrose cleavage caused by SS. Initial low ABA content and low ratios of ABA to IAA, GA and ZR, together with the GA, IAA and ZR of high-content, soluble sugars worked more efficiently to induce new bulb formation.