A Sensitive Bioassay for Gibberellins based on Retardation of Leaf Senescence in Rumex obtusifolius (L.)

Abstract. The kinetics of chlorophyll and protein decomposition and the effect of gibberellic acid (GA) were examined in senescing leaf discs of Rumex crispus and R. obtusifolius. Loss of Rumex total chlorophyll proceeds at ia s9low rate for about 2 days followed by a period of rapid logarithmic decline. Chlorophyll b is lost at a slightly faster rate than chlorophyll a during senescence in discs as well as in situ. GA causes a complete cessation of net chlorophyll and protein degradation for several days in Rumex, in contrast to the incomplete senescence inhibition generally observed with cytokinins. GA is fully effective even when added at the middle of the logarithmic phase of chlorophyll loss. Senescence inhibition by GA is apparen,tly gradually reversed upon GA removal. The cytokinins, kinetin and 6.benzylaminopurine, were also effective in Rumex leaf discs, indicating that 'the senescence retarding effect was not restricted to the gibberellins. ResultsThe time course of chlorophyll and protein loss is illustrated in figure 1. The loss of chlorophyll alwa-s shows a distinct lag phase during whllicl total chlorophyll decreases at a rate of less thin 5 % per day. After this time chlorophyll loss proceeds at a rapid pace until more than 80 % of the initial amount is degraded. Chlorophyll loss durlin this period follows a logarithmic decline. The decay of chlorophyll a and b follows a similar patterln except for the following: a more rapid drop in chlorophyll b during the lag phase; and a less rapid decrease in b toward the end of the period of chlorophyll loss.. The slightly greater rate of chlorophyll b loss during the log phase leads to an increase in the chlorophyll a :b ratio during senescence (from 32-4.6 in this case). A relativelv faster chlorophyll b decline was also measured in R. crispus leaves yellowing on the plant. 1S55www.plantphysiol.org on May 12, 2018 -Published by Downloaded from

Section: Resultsmentioning

confidence: 99%

Control of Senescence in Rumex Leaf Discs by Gibberellic Acid

Goldthwaite

Laetsch

1968

“…In many species, the most obvious symptom is yellowing of the leaves resulting from the degradation of photosynthetic pigments. In consequence, Chl content is employed widely as an index of leaf senescence, not only in the study of senescence per se, but also in the bioassay of gibberellins (15), cytokinins (6), and other growth regulators which influence senescence. In herbage plant breeding programs concerned with selection for winter greenness and extension of the climatic limits of the productive phase of leaf development (3), a subjective assessment of pigment content is often employed as a selection criterion.…”

mentioning

confidence: 99%

Separation of Chlorophyll Degradation from Other Senescence Processes in Leaves of a Mutant Genotype of Meadow Fescue (Festuca pratensis L.)

Thomas¹,

Stoddart²

1975

129

Chlorophyll levels in 1-cm sections of the youngest fully expanded leaves of normal (Y) Festuca pratensis L. declined almost to zero over a period of 6 days after excision. Chlorophyll in a mutant genotype (NY) remained near the initial level for the whole of this period. Abscisic acid promoted pigment loss in Y but had no significant effect on chlorophyll in NY. Kinetin retarded pigment loss in Y but was ineffective in NY. Other biochemical changes associated with leaf senescence-reduction in protein content and the appearance of novel isoenzymes of a-naphthyl acetate esterases-occurred in both genotypes. Abscisic acid accelerated protein breakdown, whereas kinetin inhibited the loss of protein in both genotypes. The mutation thus appears to be expressed as a highly specific lesion in pigment metabolism. We concluded that pigment breakdown, which is widely used as an index of leaf senescenice, may not be an inevitable part of the aging process.Leaf senescence is a syndrome, comprising a number of biochemical and physiological changes. In many species, the most obvious symptom is yellowing of the leaves resulting from the degradation of photosynthetic pigments. In consequence, Chl content is employed widely as an index of leaf senescence, not only in the study of senescence per se, but also in the bioassay of gibberellins (15), cytokinins (6), and other growth regulators which influence senescence. In herbage plant breeding programs concerned with selection for winter greenness and extension of the climatic limits of the productive phase of leaf development (3), a subjective assessment of pigment content is often employed as a selection criterion. In such studies, it is commonly assumed that Chl degradation is linked in an obligate fashion to all the other components of the senescence process, such as protein degradation, changes in enzyme activity, and in isoenzyme patterns (2,11,13 Plants were glasshouse-grown in shallow boxes of John Innes No. 1 compost under normal daylight supplemented as necessary with high pressure mercury vapor lighting to give a daylength of 17 hr. The youngest fully expanded leaves of plants at the 5-or 6-leaf stage were cut into 1-cm sections and kept on moist filter paper in Petri dishes (13) in complete darkness at 20 C. Before incubation, leaf sections were surface sterilized as described by von Abrams (14) and aseptic conditions were maintained throughout the incubation period.Tissue Extraction. Each sample consisted of 10 leaf sections. After weighing, the sections were homogenized in 1 ml of buffer (0.05 M tris, 0.01 M MgSO4, 2 mm GSH, 0.25 mM EDTA; pH 7.4) using a pestle and mortar. The resultant paste was centrifuged for 6 min at 12,000g to give a supernatant for soluble protein and isoenzyme determinations.Determination of Soluble Protein and Chlorophyll. Protein was determined by the Lowry procedure (9) after precipitation with 10% trichloroacetic acid. Changes in specific leaf protein components were followed by disc electrophoresis according to the methods of Davis...

“…This phenomenon is known as the "little tuber" disorder (9,22 (22) and assayed with the soybean bioassay (11). Acidic gibberellin-like compounds were extracted with ethyl acetate as previously described (5) and their levels determined with the Rumex leaf senescence bioassay (24). All extracts were strip-loaded onto Whatman No.…”

Section: Methodsmentioning

confidence: 99%

Effect of Ethylene on the Endogenous Cytokinin and Gibberellin Levels in Tuberizing Potatoes

Dimalla¹,

Staden²

1977

High concentrations of 2-chloroethylphosphonic acid inhibited tubenzation on aged potato tubers (Solanum tuberosum) that had been predisposed to the little tuber disorder. As a result of this treatment sprouts developed which contained relatively high levels of endogenous gibberellins and which elongated normally. The endogenous cytokinin levels in the different treatments did not change appreciably. It is suggested that tuberization is prevented by ethylene either as a direct inhibition of cell division or that it prevents the endogenous cytokinins from functioning. Irrespective of the mode of action of ethylene, cell division apparently is the prmary process affected, the result being that storage tisue required for the accumulation of starch is not formed.