Two new abscisic acid (ABA)-insensitive mutants of

Priming of seeds is generally intended to reduce time to germination, often leading to improved emergence. However, as a negative side effect, priming reduces longevity of seeds. We studied the possibilities to obtain primed seeds with reduced time to germination but with longevity similar to that of untreated seeds. For several species tested we found that the desired longevity could be obtained by keeping the seeds, after a priming treatment, under a mild water and / or temperature stress for a period of several hours to days. Time to germination did not increase again due to such a treatment. Optimal duration and degree of water stress were strongly temperature dependent. The methods applied to obtain primed seeds without loss of longevity are very similar to those used to induce desiccation tolerance in germinated seeds.

1994, Carbohydrates are not the sole factor determining desiccation tolerance in seeds of Arahidopsis liwliana. AB-Vdcficient iahti-l) and ,'\BA-insensitive iahi?-!) double mutant -seeds oi Ayahidapsis thaHaua are desiccation-intolerant-Carbohydrates are supposed lo fulfill a role in membrane protection during dehydration-Desiccation tolerance can be induced in double mutant seeds in \ ivo by supplying the -^BA-analog L.' VB 17,^ 711 to the pianl root system-Howe%er, this does noi lead to signiticant changes in the carbohydrate composition-In contrast, in vitro incubation of dissected immature seeds with ,AB.A induced desiccation tolerance concomitant with an increase in the seed raftlnose content. Thus, ditierent desiccation tolerance-inducing treatments show contradictor} effects on seed carbohydrate composition and accumulalion. ll is concluded that, although carbohydrates might be involved in membrane protection or giass formation during dehydration, it is nnlikeK that they are the sole factor determining desiccation toleiiince in Arahifhfp\is seeds Key wnrd.y -AB,-\-.Arahidopsis ihallatia. cai'bohydrates, desiccation tolerance-./-J. .1. Chillis Icorrcspcndini^ ainhor I and C. M. Karssen. Depl of Pianl Physiology. Wageniugeii .Ai^iicuhura! Univ.. .Arhoyeniinlaau 4. 6703 BD Wugcniiigeii. The !\'erhei'laiids: J. A. Wilmer. Center far Agnihlological Research. P.O. 14. 67iX) AA Wagentngt'ii. The Netherlands.

SUMMARY Arabidopsis thaliana mutants that were either ABA‐deficient (aba1‐1) or ABA‐insensitive (abi3‐1) and their recombinant (aba1‐1, abi3‐1) were used to determine whether ABA plays a role in the regulation of deposition of reserve material during seed development. The total net import of assimilates into seeds of these genotypes was unaffected compared to wild‐type seeds, but the distribution of these assimilates over the various types of storage material depended on the genotype. All mutants were to the same extent impaired in the synthesis of long‐chain fatty acids: their seeds contained three times less eicosenoic acid (20:1) in the triacylglycerol fraction compared to wild‐type seeds. Moreover, recombinant (aba1‐1, abi3‐1) seeds accumulated considerably less neutral lipids than wild‐type and single‐mutant seeds, and simultaneously the amounts of soluble carbohydrates and starch were increased. Absence of and insensitivity to ABA apparently cause inhibition of acyl‐chain elongation and of lipid accumulation, and as a result a higher proportion of the imported assimilates is stored as carbohydrates.

Action of endogenous abscisic acid (ABA) is absent in the ABA‐deficient and ‐insensitive double mutant (aba‐1abi3–1) seeds of Arabidopsis thaliana. Thus, responses to osmotic stress and dehydration can be studied without interference of endogenous ABA. Seeds of this double mutunt are viable hut desiceation‐intolerant. However, desiccation tolerance can he induced by either (1) slow dehydration of immature seeds; (2) treatment of immature seeds with osmotica or; (31 due to the leakiness of the ABA‐insensitivty mutation, by application of exogenous ABA. Consequently it is concluded that either ABA or osmotic‐ or dehydration‐stress and related gene expression meets the minimal requirements for acquisition of desiccation tolerance in seeds of Arabidopsis thalianna.