Regional growth patterns in the hypocotyls of etiolated and green cress seedlings in light and darkness

Abstract. A system is described whereby seedling development can be analysed in terms of growth rates of specific 1 mm regions of the hypocotyl. The technique involves time-lapse photography of marked hypocotyls in a specially designed chamber which accommodates seedlings in various orientations with respect to gravity, and under irradiation regimes differing in light quality, quantity and direction. The results of a preliminary study of the upward growth of etiolated or green cress seedlings in darkness or overhead while light are reported. Highest growth rates in etiolated seedlings were observed in zones in the upper one-third of ihe hypocotyl. In green seedlings, growth was more prominent within the subapical zones. Light further restricted growth of the median and basal zones in both types of seedling. However, in their immediate responses to the onset of irradiation, green and etiolated seedlings differed markedly. In etiolated seedlings, recovery of growth at the apex was accompanied by the development of inhibition in the median-basal regions; green seedlings showed a transient inhibition of growth in the apical zone together with a strong immediate inhibition in the median-basal regions.     

Structure and Function of the Adrenal Gland of Fishes

The structure and distribution of the adrenal gland in fishesis reviewed. Studies on the in vitro and in vivo biosynthesisof adrenocortical steroids and their occurrence in the bloodof fishes are evaluated in the light of modern techniques forthe identification and quantification of steroids. There followsan appraisal of some literature dealing with the adrenocorticalcontrol of intermediary metabolism and ion transport in fishes.     

The effects of buried magnets on colonies of Amitermes spp. building magnetic mounds in northern Australia1

ABSTRACT Unlike four control colonies of Amitermes which built normal, north-south oriented 'magnetic' mounds in northern Australia, four young colonies failed after exposure to experimental alteration of the earth's magnetic field. In November 1979, bar magnets were buried on either side at the base of each of three new nests of Amitermes laurensis Mjoberg and one new colony of A.vitiosus Hill. As controls, non-magnetized iron bars were disposed similarly in relation to three new nests of the former species and one of the latter. In September 1986, all four control nests had grown normally. However, not one of the treatment colonies survived and from what remained of the former nest in each case it is clear that the demise of the colonies occurred soon after the magnets were placed. We conclude that the failure of these colonies was the result of the changed magnetic environment. Whether 'magnetic' termites use magnetoperception as a cue to achieve their spectacular north-south orientation remains unknown, but the results of this field experiment weigh more for than against this possibility.     

Defoliation-Induced Stress in Nodules of White Clover: II. IMMUNOLOGICAL AND ENZYMIC MEASUREMENTS OF KEY PROTEINS

Changes in key nodule proteins following defoliation of whiteclover plants were assessed by measurements of enzyme activitiesand by use of antibodies to specific nodule proteins. Defoliation caused major declines in protein and leghaemoglobinlevels and in the activities of invertase, sucrose synthase,UDP glucose pyrophosphorylase, aspartate amino transferase,glutamine synthetase, phosphoenolpyruvate carboxylase, and malatedehydrogenase. In continuously defoliated plants the activities of these noduleenzymes continued to decline throughout the course of the 17d experiment. In plants defoliated once and then allowed toregrow new leaves, nodule enzyme activities declined for 7 to10 d before increasing again to control levels by the end ofthe experiment. In this single defoliation/recovery treatmentonly the activities of PEP carboxylase and glutamine synthetasedeclined to a greater extent than the general decline in proteincontent. Alcohol dehydrogenase, increased in specific activityfollowing a single defoliation and only declined in nodulesof continuously defoliated plants. Amino peptidase activity declined in concert with other enzymeactivities described above. Endopeptidase activity, in contrast,increased significantly after 4 d following either a singleor continuous defoliation. In the plants allowed to regrow newleaves endopeptidase activity declined to control levels again,whereas in plants continuously defoliated the activity rose5-fold. However, endopeptidase increased only after significantdeclines in protein and other enzyme activities had alreadyoccurred. Western immunoblotting confirmed that the declines in glutaminesynthetase activity and leghaemoglobin levels were due to thedisappearance of antigen. Declines in nitrogenase componentsI and II indicated that bacteroid proteins were affected bydefoliation over the same time-scale as host plant encoded proteins.As new leaves grew and nodule N₂ fixation was reestablished,these specific nodule proteins were again detectable by immunoblotting. Key words: Trifolium repens, white clover, defoliation, nodules, enzymes, antibodies