Free Abscisic Acid Content Research Articles

Does Seed Priming Induce Changes in the Levels of Some Endogenous Plant Hormones in Hexaploid Wheat Plants Under Salt Stress?

AbstractIn order to assess whether salt tolerance could be improved in spring wheat (Triticum aestivum L.), the present study was performed by soaking the seeds of two cultivars, namely MH‐97 (salt sensitive) and Inqlab‐91 (salt tolerant), for 12 h in distilled water or 100 mol/m3 CaCl2, KCl, or NaCl. Primed seeds from each treatment group and non‐primed seeds were sown in a field in which NaCl salinity of 15 dS/m was developed. Priming of seeds with CaCl2, followed by priming with KCl and NaCl, was found to be effective in alleviating the adverse effects of salt stress on both wheat cultivars in terms of shoot fresh and dry weights and grain yield. Priming with CaCl2 alleviated the adverse effects of salt stress on hormonal balance in plants of both cultivars. In MH‐97 plants, CaCl2 pretreatment considerably reduced leaf abscisic acid (ABA) concentrations and increased leaf free salicylic acid (SA) concentrations under both saline and non‐saline conditions. In contrast, in the Inqlab‐91 plant, CaCl2 increased free indoleacetic acid (IAA) and indolebutyric acid (IBA) content. However, priming of seeds with CaCl2 did not alter free polyamine levels in either cultivar, although spermidine levels were considerably lower in plants raised from seeds treated with CaCl2 for both cultivars under saline conditions. Priming with KCl increased growth in Inqlab‐91 plants, but not in MH‐97 plants, under saline conditions. The salinity induced reduction in auxins (IAA and IBA) was alleviated by NaCl priming in both cultivars under saline conditions. However, NaCl increased leaf free ABA content and lowered leaf SA and putrescine levels in Inqlab‐91 plants under saline conditions. In conclusion, although all three priming agents (i.e. CaCl2, KCl, and NaCl) were effective in alleviating the adverse effects of salt stress on wheat plants, their effects on altering the levels of different plant hormones were different in the two cultivars.(Managing editor: Ping He)

RELATION BETWEEN HORMONAL BALANCE AND POLYGALACTURONASE ACTIVITY IN GRAPE BERRY

Grape berry Vitis vinifera L. is a non climacteric fruit that exhibits a double sigmoidal pattern of growth. The first phase corresponds to cellular multiplication and growth. Ripening occurs concomitantly with the second growth phase and involves significant changes. Sugar accumulation and colour change are well known. Many changes in cell wall polymer properties occur during softening and the implicated mechanisms are still unclear. Abscisic acid (ABA) and indole acetic acid (IAA) levels during grape berry development have been evaluated. The free ABA content of whole berries and separated pericarp increases during the change of colour. ABA accumulation is concomitant with a peak in IAA level. ABA seems to have a specific repartition between the different tissues of the berry during the development. Our results indicate that the pulp looses its ABA during ripening. On the contrary, ABA increases in the skin tissue. Calcium ion concentration develops in the same way while the skin tissue water content decreases. ABA may be involved in protein synthesis such as cell wall-modifying enzymes. Polygalacturonase (PG) activity is detected during colour change period and seems to be well correlated with ABA levels in the berry. We also note two types of development in the PG activity profile: In several cultivars, the berries show an increase of PG activity during change colour period whereas this activity appears earlier, at the beginning of change colour process for other Bordeaux cultivars. These results are also well correlated with free galacturonic acid levels in berry must.

Abscisic acid affects floral initiation in Polianthes tuberosa

Summary Application of 5 or 25 μg abscisic acid (ABA) per plant to the upper part of corms of Polianthes tuberosa L. (cv. Double) at the vegetative stage inhibited floral initiation and plant height, especially when ABA at 25 μg per plant was applied. The contents of endogenous free ABA in corms decreased significantly at the floral initiation stage, and remained at a low level at flower development stage as compared with the vegetative stage. However, no significant changes in bound ABA levels were observed at three different growth stages of corm development. These results suggest that the dramatic reduction in the free ABA content in corm tissues are correlated with floral initiation and flower development in P. tuberosa.

Water Status and ABA Content of Floral Organs in Drought-Stressed Wheat

Chemical signals from roots have been shown to mediate the response of vegetative shoots to drought. Our objective was to test whether root signals such as abscisic acid (ABA) affect grain set in wheat. Uniculm wheat was grown in a controlled environment and exposed to a water deficit from pollen mother cell meiosis to late boot stage-a period of reproductive development very sensitive to drought. The water deficit decreased grain numbers per spike up to 70%. As soil moisture was depleted, leaf, glume, ovary and anther water potential (Ψw) decreased with leaf Ψw. Turgor decreased in the leaves, but remained at or above control levels in all floral organs examined. Free ABA content of leaves increased 30-fold as leaf turgor declined, while ABA in floral organs increased 10-15-fold. To separate the effects of shoot and root water status on grain set, plants were pressurised to maintain leaf Ψw at control levels as the soil dried. Pressurisation increased flowers and grains per spike over that of droughted plants at comparable soil water suctions, but not to control levels. Free ABA content in leaves and floral organs increased only about 3-fold when leaves were maintained at high Ψw. Shoot water status had a greater effect on grain set than did soil water status. In both pressurised and unpressurised plants, grains per spike and percentage grain set decreased with increasing ABA content in ovaries and anthers. The results indicate that maintenance of a high shoot water status reduces the effect of soil water deficit on grain set by reducing the accumulation of ABA.

Desiccation‐sensitive Hopea odorata seeds: Sensitivity to abscisic acid, water potential and inhibitors of gibberellin biosynthesis

When fruits of Hopea odorata are shed, seed water content is high. These seeds are not tolerant to desiccation and germination usually occurs within the first week after abscission. To determine the factors involved in the control of germination, isolated embryos were cultured in vitro and their sensitivity to abscisic acid (ABA), water potential and inhibitors of gibberellin biosynthesis was determined. Moreover, free ABA content was quantified by radioimmunoassay and ABA metabolism was studied by feeding [3H]‐ABA to embryos. Reproductive units of the desiccation‐sensitive seeds of Hopea odorata contain several embryos, all of which are germinable and may give, according to their developmental stages, plantlets that range from those that are prematurely developed as a result of precocious germination to those that are normal. Whatever the developmental stage, the free abscisic acid (ABA) content of the embryo was low. This low endogenous ABA and the inability of high levels of exogenously applied ABA to inhibit germination could be explained by an active ABA metabolism as demonstrated by both a rapid [3H]‐ABA turnover and the existence of high levels of endogenous conjugates. Moreover, both a decrease in the water potential of the culture medium, alone or in addition with ABA, and an inhibition of gibberellin biosynthesis, could induce a reversible inhibition of germination. Such an interaction between ABA, GA and water potential is discussed in the light of results recently reported in hormone‐deficient or hormone‐insensitive mutants.

Seed dormancy in Acer: The role of abscisic acid in the regulation of seed development in Acer platanoides L.

Germinability of isolated embryos from developing fruits of Acer platanoides was high at the earliest developmental stage assessed (90 dpa), but fell subsequently and at seed maturity was very low. These observations showed an inverse correlation with changes in endogenous free abscisic acid (ABA) levels in the embryo, which were low during early ontogeny, but reached maximum levels late in development (150–160 dpa). These observations suggest the possibility that dormancy may be induced during development as a result of ABA accumulation in the embryo, an argument strengthened by the obvious inhibitory effect of added ABA on the germinability of isolated embryos. The cotyledons appear to exert an inhibitory influence on embryo germinability that may result from their free ABA content although the embryonic axis itself possesses an innate dormancy that may reflect its own free ABA content. The increased germinability of isolated embryos resulting form added kinetin serves only to emphasise the complexity of the system and the dangers of simplistic interpretation. The correlation between germinability and ABA content is not complete, however, since much of the reduction in germinability had occurred before any appreciable increase in free ABA levels in the embryo was observed. Indeed the failure of the intact seed to respond to endogenous changes in embryonal ABA levels suggests that even though free ABA in the embryo may influence embryo germinability, it has little effect in the intact seed, where the presence of an intact testa may be a more important factor. The absence of a desiccation phase in the embryo during the late stages of development suggests that the large increases in endogenous free ABA did not cause dormancy by inhibiting water uptake, nor did they result from water stress in the embryonal tissues.

Abscisic acid and the regulation of embryo dormancy in the genus Acer.

Germination of Acer pseudoplatanus L. and Acer platanoides L. seeds was increased by moist storage of the intact fruits (seed + pericarp) at 5 degrees C, but not at 17 degrees C. In both species, germinative capacity of isolated embryos (seeds with testa removed) was increased by moist storage of fruits at either 5 or 17 degrees C. Thus dormancy loss by intact seeds and excised embryos was not necessarily correlated. Loss of dormancy in isolated embryos was associated with a reduction in free abscisic acid (ABA) content. Embryos from freshly harvested fruits of A. pseudoplatanus had a higher germinative capacity and a lower free ABA content than embryos from freshly harvested fruits of A. platanoides. Morever, germinative capacity increased, and free ABA content decreased, more rapidly with length of fruit storage in A. platanoides embryos than in A. pseudoplatanus embryos.

Inverse Correlation between ABA Content and Germinability throughout the Maturation and theIn VitroCulture of the Embryo ofPhaseolus vulgaris

Prevost, I. and Le Page-Degivry, M. Th. 1985. Inverse correlation between ABA content and germinability throughout the maturation and the in vitro culture of the embryo of Phaseolus vulgaris.—J. exp. Bot. 36: 1457–1464. Changes in embryo abscisic acid (ABA) content during the maturation of the seed of Phaseolus vulgaris cv. Contender were followed, using a radio-immunoassay. The pattern of change is similar to that already described in several species: a rapid increase (from the 18th to 29th day after anthesis), was followed by a decrease, the ABA level being ten times lower on the 48th day than on the 29th. Embryos isolated from the 18th to the 48th day after anthesis were able to ‘germinate’ when cultivated on a mineral medium supplemented with sucrose and agar. The development pattern varied throughout the embryogenesis and could be correlated with the differentiation of the embryo at the time of isolation. Before germination could take place, we observed a lag phase, the duration of which could be correlated with embryo ABA content. As ABA content increased in the youngest embryos the duration of the lag phase increased. In the same way, the number of days to germination was shown to diminish as ABA content decreased. Inverse correlation between ABA content and germinability was thus demonstrated throughout the development of the embryo. During in vitro culture, free ABA content decreased in the embryo and reached low values a few days before germination occurred. So the beginning of root elongation in culture was again well correlated with the disappearance of free endogenous ABA. A transfer experiment inducing an earlier germination associated with a more limited development suggests that the lag phase is associated with an active continuation of embryonic development

Relationship Between Changes in Abscisic Acid and Ethylene Production During Ripening of Avocado Fruits

Abscisic acid levels and the rates of ethylene production during successive stages of ripening in avocado fruits (Persea americana Mill.) were determined by gas chromatography. In fruits which were selected for abscisic acid determination according to their rate of ethylene production, a rise in free abscisic acid content was observed following an increase in the rate of ethylene production. Levels of bound abscisic acid were much lower and increased later than free abscisic acid.