William M. Proebsting

Feed-back regulation of gibberellin biosynthesis and gene expression in Pisum sativum L.

Treatment of tall and dwarf (3β-hydroxylase impaired) genotypes of pea (Pisum sativum L.) with the synthetic, highly active gibberellin (GA), 2,2-dimethyl GA4, reduced the shoot contents of C19-GAs, including GA1, and increased the concentration of the C20-GA, GA19. In shoots of the slender (la crys) mutant, the content of C19-GAs was lower and GA19 content was higher than in those of the tall line. Metabolism of GA19 and GA20 in leaves of a severe (na) GA-deficient dwarf mutant was reduced by GA treatment. The results suggest feedback regulation of the 20-oxidation and 3β-hydroxylation reactions. Feed-back regulation of GA 20-oxidation was studied further using a cloned GA 20-oxidase cDNA from pea. The cDNA, Ps074, was isolated using polymerase chain reaction with degenerate oligonucleotide primers based on pumpkin and Arabidopsis 20-oxidase sequences. After expression of this cDNA clone in Escherichia coli, the product oxidized GA12 to GA15, GA24 and the C19-GA, GA9, which was the major product. The 13-hydroxylated substrate GA53 was similarly oxidized, but less effectively than GA12, giving mainly GA44 with low yields of GA19 and GA20. Ps074 hybridized to polyadenylated RNA from expanding shoots of pea. Amounts of this transcript were less in the slender genotype than in the tall line and were reduced in GA-deficient genotypes by treatment with GA3, suggesting that there is feed-back regulation of GA 20-oxidase gene expression.

Response ofNp mutant of pea (Pisum sativum L.) to pea weevil (Bruchus pisorum L.) oviposition and extracts

TheNp mutant of pea (Pisum sativum L.) is characterized by two physiological responses: growth of callus under pea weevil (Bruchus pisorum L., Coleoptera: Bruchidae) oviposition on pods, and formation of neoplastic callus on pods of indoor-grown plants. Although these two responses are conditioned byNp, they are anatomically and physiologically distinguishable, based on sites of origin, distribution pattern, and sensitivity to plant hormones. Further characterization of the response to extracts of pea weevil showed that response of excised pods, measured by callus formation, was log-linear, and treatment with as little as 10−4 weevil equivalents produced a detectable response. Mated and unmated females contained similar amounts of callus-inducing compound(s), and immature females contained significantly less of the compound(s). Female vetch bruchids (Bruchus brachialis F., Coleoptera: Bruchidae), a related species, contained callus-inducing compound(s), but usually less than pea weevils on a per weevil basis. Males of both species contained less than 10% of the activity of the mature females. Extracts of female black vine weevils, a nonbruchid species, did not stimulate callus formation. Based on partitioning and TLC analysis, the biologically active constitutent(s) was stable and nonpolar. Thus, theNp allele probably conditions sensitivity to a nonpolar component of pea weevil oviposition as a mechanism of resistance to the weevil.

The Relationship of [3H]GA9 Metabolism to Photoperiod-induced Flowering in Pisum sativum L.

Summary The late flowering line of pea designated G is an obligate long day plant with respect to flowering. [3H]GA9 metabolism by leaves of G was studied. In short days (SD), [3H]GA9 was converted to a series of polar compounds. The synthesis of these polar compounds was blocked by 1 long day (LD). One LD also induced flowering. Reproductive G plants which reverted to the vegetative state regained the ability to synthesize polar gibberellins from [3H]GA9. These observations support the hypothesis that flowering in Pisum is inhibited by a polar gibberellin produced in SD. LD prevent the synthesis of polar gibberellins, permitting flowering to take place.

Transmissible Factors Regulating Shoot Growth of Cornus sericea L.

Summary The regulation of shoot growth of Cornus sericea L. by photoperiod and plant growth regulators was studied. In Cornus , short days (SD) induce dormancy; long days (LD) favor continued shoot growth. When plants were grown with one branch in SD and one branch in LD, a dormancy-inducing stimulus from a foliated branch in SD caused a dormant bud to form on a defoliated branch in LD. Conversely, growth promoters from a foliated branch in LD prevented dormancy in a defoliated branch in SD. A single pair of SD leaves induced dormancy in a plant in LD if no LD leaves were between the SD leaves and the apex. Exogenous abscisic acid did not induce dormancy in LD; GA 3 (1 mM), translocated from treated leaves prevented dormancy in SD. Ancymidol (20 μmol) induced dormancy in LD. Gibberellins were implicated as dormancy regulators in Cornus . Translocation is discussed as a criterion for assessing the possible role of growth regulators in dormancy.