Effect of abscisic acid on the transport of assimilates in barley

The effect of abscisic acid (ABA) on assimilate transport in barley was investigated in two parallel experiments. First, the effect upon [¹⁴C]sucrose transport from the flag leaf to the ear of a single ABA application made at different stages of growth of the fruits was investigated; the effect was measured 24 h after treatment. Second, the effect of a single application of ABA made at the same stages of growth as above on grain weight of the mature plant was investigated. In both types of experiments ABA was applied once to the ear of different plants as an aqueous solution (10^-3–10^-5 M), one to five weeks after anthesis. [¹⁴C] sucrose was applied by means of agar blocks. Parallel to these experiments, the endogenous content of ABA was investigated in the developing grains. When ears were treated with ABA two or four weeks after anthesis, an increase of up to 70% in the ¹⁴C-transport from the flag leaf to the ear was observed within a 24-h period after treatment (short duration experiments). At these growth stages the endogenous concentrations of ABA were low. In sharp contrast, ABA, especially in a concentration of 10^-3 M, decreased ¹⁴C-import from the flag leaf when applied three weeks after anthesis. At this stage the endogenous ABA content had reached its maximum. Long duration experiments with a single application of ABA to the car two weeks after anthesis resulted in a marked increase of weight per thousand kernels. ABA applications made earlier or later than two weeks after anthesis either reduced the grain weight or had no effect. It is concluded that ABA is involved in the regulation of assimilate transport from the leaves to the grains, possibly by influencing the unloading of sieve tubes in the ears. Promotion or inhibition of assimilate import by exogenously applied ABA may depend on the developmental stage of the grains and on the endogenous ABA level.Abbreviations ABA abscisic acid - TKW weight per thousand kernels     

Abscisic acid in developing grains of wheat and barley genotypes differing in grain weight

Two genetically related wheat lines growing in cabinets were given different temperatures during grain filling, and abscisic acid (ABA) was measured in whole grains by gas chromatography with an electron-capture detector. Three genetically related barley lines grown in the field were assayed for ABA content in endosperm and embryo fractions separately by radiommunoassay.Maximum grain growth rate and final weight per grain of the two wheat lines differed by 50–60% at low temperature and 30–40% at high temperature. During grain development two peaks in ABA level were observed at low temperature but only one at high temperature. At times when differences in grain growth rate between genotypes and between temperature treatments were large, the corresponding differences in ABA concentration were small. In barley, one line (Iabo 14) had 30% heavier grains than the other two (Onice and Opale). Endosperm ABA concentrations showed no clear differences between genotypes until grain filling was nearly complete. Embryo ABA levels were up to 10-times greater than those in the endosperm, with Opale having significantly less ABA in the embryo than the other two cultivars.Our experiments did not provide evidence for a causal relationship between ABA levels during grain filling and grain growth rate or final weight.Abbreviations ABA Abscisic acid - DAA days after anthesis - DW dry weight - FW fresh weight     

Plant growth regulation with triazoles of the dioxanyl type

The plant growth retarding activities of several dioxanylalkyl and dioxanylalkenyl triazoles were determined in seedlings of barley, rice, and oilseed rape. Out of these groups some substances proved to be among the most efficient growth retardants known. The compound 1-(4-trifluormethyl)-2-(1,2,4-triazolyl-(1))-3-(5-methyl-1,3-dioxan-5-yl)-propen-3-ol was investigated more closely. Shoot growth is reduced more intensively than root growth by this compound. At lower dosages root growth may even be stimulated. The action of this retardant can be antagonized by gibberellin A₃ and byent-kaurenoic acid. It is suggested that its main biochemical action is to block the reactions that lead froment-kaurene toent-kaurenoic acid in the course of gibberellin biosynthesis.     

Abscisic Acid Translocation and Influence of Water Stress on Grain Abscisic Acid Content

The movement of foliar applied [1-¹⁴C]abscisic acid (ABA) inwheat plants (Triticum aestivum L., cv. Kolibri) was investigatedat two stages of grain development (1000 grains, weight 19 and24 g dry matter). [1–¹⁴C]ABA seemed to be readily translocated within 12h into the developing grains as well as in other plant parts.A subsequent rapid metabolism took place leading to a decreasedactivity of the ABA-containing chromatogram fraction in theyounger plants 48 h after application. The metabolism seemodto be less intensive in the older grains, where the activityrunning with the ABA increased over 64 h. Treating the leaves of barley plants (Hordeum vulgare, L., cv.Union) 2 weeks after anthesis with a gentle stream of warm air(36° C) resulted in a significant increase in the ABA contentof all parts of the ear. The results mentioned above indicatethat this may be partially due to translocation from other partsof the plant such as the leaves.     

Regulation by kinetin and abcisic acid of correlative senescence in relation to grain maturation,source-sink relationship and yield of rice (Oryza sativa L.)

When kinetin was applied to the source organ (flag leaf) of rice (Oryza sativa L. cv. Ratna), foliar senescence was delayed and grain yield per plant (as evidenced by grain weight, grain/straw weight ratio and 1,000 grain growth) was increased through the increase of sink activity (increase in dry weight of the grains/plant), duration of sink capacity as well as photosynthetic ability of the glumes (as determined by the chlorophyll content of the glumes of the developing grains). However, application of kinetin to the sink organs (fruits), promoted senescence of the source but increased the yield by increasing the sink capacity and 1,000 grain growth mostly at the earlier stage of reproductive development. Lower sterility percentage was associated with higher grain yield of the plant by kinetin treatments. ABA applied either to the source or the sink promoted leaf senescence and reduced the grain yield by reducing the sink activity, harvest index, sink capacity duration and increasing the sterility percentage. Thousand grain dry weight at harvest did not vary significantly amongst the treatments. It was concluded that nutrient drainage was associated with the correlative influence of fruit on the monocarpic senescence of rice plant and that a competetion for differential allocation of cytokinin and ABA in the source and sink organs initiates this senescence syndrome.     

Effects of seed treatment with a plant growth regulator on growth and tillering in spring barley (Hordeum distichum) cv. Triumph

Doses of the growth retardant, Terpal, were applied to seeds of spring barley. Germination was delayed as the concentration and duration of exposure to Terpal increased. Tiller bud outgrowth was promoted in treated seedlings and at maturity the total tiller production and number of ear-bearing tillers per plant was increased by the Terpal treatment. The yield of the main shoot was similar in both control and treated plants but the mean ear weight of the tillers was reduced in the latter, and thus there was no overall effect of the treatment on yield. Observations on vegetative plants showed that Terpal also reduced the growth of successive main shoot leaves and the elongation and dry weight of the seminal root system. The results are discussed in terms of an early modification in the distribution of resources during establishment that favour the outgrowth of tiller buds at the expense of the initial development of the main shoot and root system. It is proposed that seed treatment is a viable alternative to foliar spraying particularly in arid regions.     

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.     

Antagonism of some gibberellin actions by a substituted pyrimidine

From a comparison of the effects of seven growth retardants and abscisic acid (ABA) on various growth systems, it was found that the gibberellin-regulated growth of lettuce hypocotyls was uniquely inhibited by the growth retardant, α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidine methanol (EL-531). Auxin-regulated growth of coleoptile sections was inhibited by Phosfon and only slightly by EL-531 and Alar. Cytokinin-regulated growth of Xanthium cotyledons showed little or no inhibition by any of the retardants. ABA was inhibitory in all three types of tests. The distinctive effects of EL-531 against gibberellin-stimulated growth and the general ability of gibberellic acid to relieve EL-531 inhibition suggest that this retardant acts in part against the gibberellin-stimulated growth system, but at a locus which discriminates between growth and nongrowth functions of gibberellic acid. It shows little or no antagonism of gibberellin actions which do not involve growth: the barley endosperm test and the Rumex leaf senescence test.     

Plant growth regulation with triazoles of the dioxanyl type

The plant growth retarding activities of several dioxanylalkyl and dioxanylalkenyl triazoles were determined in seedlings of barley, rice, and oilseed rape. Out of these groups some substances proved to be among the most efficient growth retardants known. The compound 1-(4-trifluormethyl)-2-(1,2,4-triazolyl-(1))-3-(5-methyl-1,3-dioxan-5-yl)-propen-3-ol was investigated more closely. Shoot growth is reduced more intensively than root growth by this compound. At lower dosages root growth may even be stimulated. The action of this retardant can be antagonized by gibberellin A₃ and byent-kaurenoic acid. It is suggested that its main biochemical action is to block the reactions that lead froment-kaurene toent-kaurenoic acid in the course of gibberellin biosynthesis.     

Abscisic acid in developing wheat grains and its relationship to grain growth and maturation

Summary During the later stages of growth of grains of wheat (Triticum aestivum L. cvs. WW15 and Gabo) there is a dramatic increase (up to 40fold) in the content of abscisic acid (ABA) to 4–6 ng per grain. This level remains high from 25 to 40 days after anthesis. Then, in association with natural or forced drying of the grain, there is a rapid drop (5–10 fold) in the ABA content and a brief increase in the content of bound ABA. The bulk of ABA in an ear was in the grain (95%) and although the embryo contributed 19% of this ABA it was less than 5% of the grain by weight. There was no clear relationship between ABA content and the growth of grains in various spikelet or floret positions. Application of (±)-ABA to the ear had no effect on grain growth rate but led to an earlier cessation of grain growth and hastened the drying of the grain. Isolated embryos and whole grains were capable of germinating during the mid grain growth period (15–25 days), but germination capacity declined subsequently as ABA accumulated. Later, still, with grain drying and loss of ABA, embryo and grain became germinable again. At this time there was also a dramatic increase in the ability of the grain to synthesize -amylase. It is suggested that the accumulation of ABA at the later stages of grain growth prevents precocious germination and premature hydrolysis of starch reserves of the morphologically mature but still unripe grain. An inevitable consequence of such action may be in triggering grain maturation.     

Regulation of leaf senescence, grain-filling and yield of rice by kinetin and abscisic acid

Senescence of rice ( Oryza sativa L. cv. Jaya) leaves was regulated with kinetin and abscisic acid (ABA) sprays at the reproductive stage. The effect of such sprays on grain-filling and yield was analyzed. Spraying 100-day-old plants with kinetin solution (100 μg ml^-1) significantly delayed senescence as indicated by higher total chlorophyll and protein levels in the three uppermost leaves compared with the controls. In contrast, spraying with ABA (15 μg ml^-1) significantly promoted foliar senescence. The number of spikelets per panicle, number of panicles, percentage filled grains, panicle weight and grain yield per plant and the mobilization and harvest indices were significantly increased by kinetin treatment, while ABA decreased most of them. The possibility of increased grain-filling and thus, yield due to delayed foliar senescence by kinetin treatment and decreased grain-filling due to hastening of senescence by ABA is discussed.     

Inhibition of Abscisic Acid Biosynthesis in Cercospora rosicola by Inhibitors of Gibberellin Biosynthesis and Plant Growth Retardants

The fungus Cercospora rosicola produces abscisic acid (ABA) as a secondary metabolite. We developed a convenient system using this fungus to determine the effects of compounds on the biosynthesis of ABA. Inasmuch as ABA and the gibberellins (GAs) both arise via the isoprenoid pathway, it was of interest to determine if inhibitors of GA biosynthesis affect ABA biosynthesis. All five putative inhibitors of GA biosynthesis tested inhibited ABA biosynthesis. Several plant growth retardants with poorly understood actions in plants were also tested; of these, six inhibited ABA biosynthesis to varying degrees and two had no effect. Effects of plant growth retardants on various branches of the isoprenoid biosynthetic pathway may help to explain some of the diverse and unexpected results reported for these compounds. Knowledge that certain inhibitors of GA biosynthesis also have the ability to inhibit ABA biosynthesis in C. rosicola indicates the need for further studies in plants on the mode of action of these compounds.     

Growth-regulating activity of <Emphasis Type="Italic">N</Emphasis>-benzyl- and <Emphasis Type="Italic">O</Emphasis>-benzyl-containing compounds belonging to a new group of synthetic analogues of natural auxins

We studied the effect of benzylamine, benzyl alcohol, and their derivatives (constituting a new group of synthetic analogues of natural auxins) on rooting of leaf and stem cuttings, rhizogenesis and growth of barley plantlets and tomato seedlings, and tomato plant productivity. These compounds promoted rooting of leaf and stem bean cuttings, increased rhizogenic activity, and stimulated the development of root systems in barley and tomato seeds. The activity of the compounds studied was similar to that of standard substances (3-indoleacetic acid potassium salt and 2-naphthylacetic acid). The benzyl group attached to the oxygen or nitrogen atom was shown to be the smallest molecular structure which provided auxin activity of the compounds. Derivatives of benzyl alcohol containing the quaternary ammonium fragment possessed auxin and anti-gibberellin (retardant) properties. They were selected by chemical synthesis of low-molecular-weight bioregulators with desired properties (a combination of chemical fragments with complementary physiological activity in the molecule). Auxin and anti-gibberellin (retardant) activities produced a synergistic effect. Germination of seeds treated with these compounds was accompanied by a more significant increase in the weight and length of roots (compared to standard auxins). The rate of seedling establishment reached 100%. The development of fruits and accumulation of reserve nutrient substances were synchronized and accelerated after spraying vegetating plants with solutions of studied compounds. The synergistic effect underlay a significant increase in the amount and quality of the crop (e.g., tomatoes).Translated from Prikladnaya Biokhimiya i Mikrobiologiya, Vol. 41, No. 2, 2005, pp. 243–249.Original Russian Text Copyright © 2005 by Gafurov, Makhmutova.     

Exogenous ABA Increases Yield in Field-Grown Wheat with Moderate Water Restriction

Water stress is one of the most important environmental factors that regulate a plant’s growth and development. In agronomic practice the effects of water stress are translated into low yield and/or reduced quality. Abscisic acid (ABA) sprays (1 mM) were applied to wheat plants at different phenological stages and the effects on several physiological variables and on yield were evaluated under field conditions at different water regimes. Studies were conducted in the field across three consecutive winter–spring seasons. ABA treatments were applied at the beginning of shoot enlargement and repeated at anthesis. Exogenous ABA increased shoot dry weight and maintained a high concentration of photosynthetic pigments for a longer period of time during grain growth and maturation. Although ABA applications increased stomatal closure immediately after its application, the longer-term effect was to allow for a greater ostiolar opening of the stomatal pore which resulted in increased conductance of gases and water vapor. ABA also improved the transport of photoassimilates from the leaves and stem to the developing grains, that is, it effectively increased the sink strength of the grains. This correlated with a yield increase without significantly changing the protein quality in the grains. Thus, elevated ABA levels from exogenous application or genetic selection could help improve agricultural production of grains in arid areas where irrigation is not possible.     

Dynamic Changes of Endogenous Plant Hormones in Rice Grains in Different Parts of Panicle at Grain filling Stage

The grain fresh weight and grain-filling rate at early grain developing stage in rice ( Oryza sativa L. ) were higher in the upper than in the lower part of panicle during grain filling. The grains in the upper and/or the lower part of panicle were analyzed for the endogenous plant hormones. The results indicated that the peak content of ABA and/or GA1 + 3 in the developing grains appeared at about the same stage when the highest increasing rate of grain appeared in the upper and in the lower part of the panicle respectively. After heading, the IAA content in developing grains steadily decreased in both the upper and the lower part of the panicle, GAn + 7 content decreased at first and then increased, and again decreased. At the early grain-filling stage, the ABA and GA1 + 3 contents in the developing grains were higher in the upper than in the lower part of the panicle. The role that the hormones play in the developing grains and the reason why the grains seed set better in the upper than in the lower part of the panicle were discussed.     

Effects of abscisic acid (ABA) on grain filling processes in wheat

The effect of in situ water stress on the endogenous abscisic acid (ABA) content of the endosperm and the in vitro application of ABA on some important yield regulating processes in wheat have been studied. Water stress resulted in a marked increase in the ABA content of the endosperm at the time close to cessation of growth. Application of ABA to the culture medium of detached ears reduced grain weight. Exogenously applied ABA, at the highest concentration (0.1 mM) reduced transport of sucrose into the grains and lowered the starch synthesis ability of intact grains. In vitro sucrose uptake and conversion by isolated grains was stimulated by low ABA concentrations (0.001 mM) in the medium but was inhibited by higher concentrations. ABA application had no effect on sucrose synthase (SS) and uridine diphosphate glucose pyrophosphorylase (UDP-Gppase) activities, whereas adenosine diphosphate glucose pyrophosphorylase (ADP-Gppase), soluble starch synthase (SSS), and granule-bound starch synthase (GBSS) activities were reduced. These results raise the possibility that water stress-induced elevated levels of endogenous ABA contribute to reduced grain growth.     

二棱啤酒大麦杂种一代及其亲本主要性状的灰色系统分析

研究采用灰色关联分析方法,对20组二棱型啤酒大麦杂种一代及其亲本的7个主要性状之间的关联系数、关联度和关联序进行了分析。结果表明：在关联度和关联序中,大麦的穗粒数、穗粒重,千粒重分别与穗长这一性状的关联度最大,关联序中穗长全排在首位;而穗粒数,穗粒重,千粒重分别与有效穗数这一性状的关联度最小,关联序中有效穗数全排在末位,为了提高单株产量应注意协调好有效穗数与穗长这一对主要矛盾明确各性状对籽粒产量所起的直接和间接作用及其相对重要性,确定主攻方向,配制各种优势组合。为大麦亲本选配提供科学依据。从而达到二棱型啤酒大麦预期的育种目标。     

Investigation of a His-rich arabinogalactan-protein for micronutrient biofortification of cereal grain

The micronutrient content of most cereal grains is low and responsible for malnutrition deficiencies in millions of people who rely on grains as their primary food source. Any strategy that can increase the micronutrient content of grain will have significant benefits to world health. We identified a gene from barley encoding a cell wall protein with multiple histidine (His)-rich motifs interspersed with short arabinogalactan-protein (AGP) domains and have called it Hordeum vulgare His-rich AGP (HvHRA1). Sequence analysis shows that His-rich AGPs are rare in plants and that the number of His-rich and AGP domains differ between cereals and dicots. The barley and wheat encoded proteins have more than 13 His-rich domains, whereas the putative rice orthologue has only 5 His-rich regions. His-rich motifs are well-established metal-binding motifs; therefore, we developed transgenic (Tx) rice plants that constitutively overexpress barley HvHRA1. There was no significant effect on plant growth or grain yield in Tx plants. Purification of AGPs from wild-type and Tx plants showed that only Tx plants contained detectable levels of a His-rich AGP. Calcein assay shows that the AGP fraction from Tx plants had increased binding affinity for Cu(2+) . Micronutrient analysis of brown and white rice showed that the grain nutrient yield for Fe, Zn and Cu was higher in two Tx lines compared to their respective nulls, although the differences were not statistically significant. This approach highlights the potential of the plant apoplast (cell wall) for storage of key nutrients through overexpression of genes for metal-binding proteins.     

水稻结实过程中穗不同部位谷粒中内源激素的动态变化

水稻（ＯｒｙｚａｓａｔｉｖａＬ．）结实期间,穗上部谷粒的粒重比穗下部谷粒的高,灌浆前期的增重速率比穗下部谷粒的高,在整个灌浆过程中增重速率的变化比穗下部谷粒的快。利用ＥＬＩＳＡ方法对穗上部谷粒和穗下部谷粒中各种内源激素含量的分析表明,在灌浆过程中,谷粒中未检测出ｉＰＡｓ;在穗上部谷粒和穗下部谷粒中,ＡＢＡ和ＧＡ(１＋３)的含量的最大值出现的时间分别与穗上部谷粒和穗下部谷粒增重最快的时间基本一致,无论穗上部谷粒还是穗下部谷粒中,ＩＡＡ的含量基本上均呈下降趋势;ＧＡ(４＋７)的含量是先上升、后下降、再上升;在结实的前中期,谷粒中ＡＢＡ、ＧＡ(１＋３)的含量基本上均是穗上部谷粒高于穗下部谷粒。探讨了各种激素在谷粒灌浆过程中的作用及从激素的角度探讨了穗上部谷粒比穗下部谷粒结实性好的原因。