Interaction of polyamines and light on biochemical processes involved in leaf senescence

Abstract The rapid senescence of detached oat leaves in darkness is first manifested by a sharp rise in RNase activity (about 50% within 1 h), then by a rise in protease activity (indicated by an increase in non-protein α-amino nitrogen within 6 h) and ultimately by chlorophyll degradation (beginning after 18 h). These degradative changes are delayed or prevented by low concentrations (1–10 mM) of the naturally-occurring polyamines cadaverine, putrescine, spermidine and spermine. The tetraamine spermine is generally more active than the triamine spermidine, which is in turn more active than the diamines putrescine and cadaverine. All the polyamines are more active than kinetin or cycloheximide. As little as 10 min of exposure to 1 mM spermine, especially at the beginning of the dark period, produces a marked retardation of chlorophyll degradation over a 48 h period, and 60 min of exposure saturates the effect. In the light, all polyamines promote, rather than retard, the disappearance of chlorophyll but, as in the dark, they inhibit the rise in RNase and non-protein α-amino nitrogen. The photobleaching of chlorophyll in the presence of polyamines is proportional to the duration of exposure to high irradiance (16.5 Wm^?2) fluorescent light. Such light is more effective toward the end of the 48 h post-excision test period than at the beginning. Calcium ion (1–10 mM) supplied together with the polyamines diminishes their action in dark and light, indicating probable involvement of an initial ionic attachment mechanism. The loss of chlorophyll from the leaves of four species of dicotyledonous plants (pea, bean, rape, tobacco) in the darkness is similarly retarded by 1–10 mM polyamines. In rape, the most rapidly senescing species, 1 mM spermine almost completely arrests chlorophyll degradation over a 96 h period. It is suggested that polyamine metabolism in plants may be related to normal physiological control mechanisms as in microorganisms and animals, and that polyamines could find use as anti-senescence agents for plants.     

Respiratory Responses in Potato Tubers as an Index of the effect of Ethylene Chlorhydrin and Ammonium Thiocyanate

1. The variety Phulwa was worked upon for respiratory studiesandgrowth response to dormancy-breaking hormones. The hormoneswere used in single and double doses.
2. The respiratory studiesreveal that ethylene chlorhydrin affectsonly the bud areasand not the non-bud areas.
3. The intensity of the effect ofthe hormone progressively decreasesin the deeper layers ofcells, till finally no effect is visiblein the cells of thepith areas.
4. A distinct correlation exists between the respiratoryintensityand dormancy.
5. Of the two hormones used the respiratoryrates recorded forN. ethylene chlorhydrin treated tubers, givenin single anddouble doses, were the highest. Similarly thegrowth responseto both the doses showed the maximum reductionof the dormancyperiod, 01 N. ethylene chlorhydrin treatmentswere not effectivein breaking the dormancy or in significantlyaltering the rateof respiration.
6. Treatments with 05 percent, ammonium thiocyanate given insingle dose showed the lowestrespiratory rates and the germinationrecords showed no differenceover the control. With the doubledose a gradual rise in therespiratory rates was observed. Thegermination records alsoshowed an earliness of 20 and 22 daysover the control and single-dosetreatments respectively.
7. Treatments with 2 per cent, ammoniumthiocyanate depressed germination.The respiratory rates recordedwere also low.
8. In general the double-dose treatments showedbetter resultsthan the single-dose treatments. Also, treatmentson 3 weeksold tubers were more effective than on 6 weeks oldtubers.