Hormonal Control of Nuclease Level in Excised Avena Leaf Tissues1

Plants of the wilty tomato (Lycopersicum esculentum) mutant,flacca, and of the normal cultivar Rheinlands Rubm growing under either "normal" or high humidity were used in this research. Under normal humidity, RNase activity was much higher in mutant plants in which abscisic acid (ABA) and water content were lower than in the normal plant. The mutant also contained less RNA and protein per cell and less soluble RNA relative to ribosomal RNA as compared with the normal genotype. In ABA-treated mutant plants, RNase activity decreased while RNA, protein, the ratio of soluble to ribosomal RNA and water content increased.Under high humidity, RNase activity in mutant plants was decreased, but was still somewhat higher than that in the normal plant, although water saturation deficit was equal in both plant types. Abscisic acid increased RNase activity in the mutant plants. The content of RNA and protein per cell was similar in both types, but the ratio of soluble to ribosomal RNA remained lower in the mutant. In ABA-treated mutant plants, although the content of DNA and RNA per fresh weight was similar to that of control mutant plants, the ratio of RNA to DNA decreased significandy. In addition, ABA caused an increase of the soluble to ribosomal RNA ratio toward the normal value in mutant plants.Contrary to ABA, kinetin increased RNase activity in the mutant under normal humidity and decreased it under high humidity.A similar incorporation of labeled uridine into RNA in normal, mutant, and ABA-treated mutant plants under normal humidity suggests that the difference between mutant and normal plats in respect to total, soluble, and ribosomal RNA results not from a different rate of RNA synthesis but from a different rate of RNA degradation, ie. RNase actvity.An increase of RNase activity (1,6,7,9,12,35) and a decrease of RNA level (8,12) was found in tomato and other plants subjected to water stress. The soluble fraction of RNA increased while the ribosomal fraction decreased in sugar beet under water stress (25). Low relative humidity appears to be associated with slow accumulation and reduced incorporation of labeled uracil into RNA in etiolated leaves of Jack bean (3).An association between RNase activity, RNA level, and hormone balance in the plant was also reported. Srivastava (29) found an increase of RNase activity in detached barley leaves treated with ABA and a decrease of this activity following treatment with kinetin. Similar hormonal effects on RNase activity were reported in other plants (5,13,28,39 The first attempt to elucidate the interrelations among RNase activity, water content, and hormone balance was made by Arad et al. (1). They found that in barley leaves, in which the water balance was not disturbed, ABA increased and kinetin decreased RNase activity. However, these hormonal effects were inverted in leaves subjected to water shortage i.e. ABA decreased and kinetin increased the activity. They interpreted these results to mean that above a certain optimal leaf water content, the specific ho...

supporting

confidence: 66%

“…Srivastava (29) found an increase of RNase activity in detached barley leaves treated with ABA and a decrease of this activity following treatment with kinetin. Similar hormonal effects on RNase activity were reported in other plants (5,13,28,39 The first attempt to elucidate the interrelations among RNase activity, water content, and hormone balance was made by Arad et al (1). They found that in barley leaves, in which the water balance was not disturbed, ABA increased and kinetin decreased RNase activity.…”

mentioning

confidence: 52%

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato

Puri¹,

Tal²

1977

“…An important component of the senescence-induced changes may well be an increased activity of ribonuclease (Table II), which has been shown to cause lysis of protoplasts (14), and to interfere with RNA precursor incorporation, as indicated by the present results. A high rate of RNase activity in senescing protoplasts is not unexpected, since wounding and senescence have been shown to increase RNase activity in many plants (5,10,22,23). Additional evidence is that pretreatment of oat leaves with cycloheximide and kinetin, which are known to prevent senescence-induced increase in RNase activity (5,17), increased protoplast stability (9).…”

Section: Discussionmentioning

confidence: 98%

“…The incorporation of tritiated L-leucine and uridine into trichloroacetic acid-insoluble materials of protoplasts was studied by the methods of Mans and Novelli (11) as described previously (6). Briefly, 0.5-ml aliquots of protoplast suspension were incubated with 20 ,ul of either 10 ,ACi/ml Lleucine ( [4,5- (23). Half-ml-aliquots of protoplast suspensions were centrifuged for 8 min at 50g in a clinical centrifuge.…”

Section: Methodsmentioning

confidence: 99%

Stabilization of Oat Leaf Protoplasts through Polyamine-mediated Inhibition of Senescence

Altman¹,

Kaur‐Sawhney²,

Galston³

1977

168

Protoplasts isolated from Avena sativa L. leaves undergo progressive senescence when incubated aseptically in 0.6 M mannitol with or without added nutrients. This senescence is manifested by morphological deterioration and ultimate iysis of protoplasts, by a decrease in incorporation of [3HJuridine and I3Hlleucine into macromolecules, and by a sharp increase in ribonuclease activity.The presence in the incubation medium of L-arginine, L-lysine, certain polyamines related to these amino acids (cadaverine, putrescine, spermidine), Ca2+, or streptomycin stabilizes the protoplasts. Protoplasts incubated with 10 mM L-arginine or L-lysine show an initial inhibition of [3Hluridine incorporation, but with time, incorporation is restored to levels greater than in control protoplasts. The rise in ribonudease activity of protoplasts is completely inhibited if the protoplasts are incubated with 10 mM L-arginine. Greater incorporation of I3Hluridine into RNA of aging protoplasts is also maintained by appropriate concentration of cadaverine, putrescine, spermidine, Ca2+, or streptomycin in the incubation medium; the same concentrations of these substances stabilize the protoplasts against additional lysis.Isolated plant cells and protoplasts in culture usually have a shorter life span than similar cells in the intact plant, and tend to undergo senescence rapidly. In a few plant species, including asparagus, rape, carrot, petunia, and tobacco (2, 3), protoplasts are capable of cell wall formation, cell division, and even regeneration of entire plants. By contrast, protoplasts of cereals, legumes, and other economically important plants do not readily divide. With regard to oat leaf protoplasts, it has been suggested that morphological instability and deterioration are related to a complex of senescence-induced changes following leaf excision and isolation of protoplasts from mesophyll cells (6, 9; Galston et al., unpublished). Apart from their morphological instability, nondividing protoplasts also show a time-dependent decline in incorporation of precursors into protein and RNA (4,6,20), and an increase in ribonuclease activity and consequent breakdown of endogenous RNA (9,20; Galston et al., unpublished).Previous experiments have established that pretreatment of excised oat leaves with cycloheximide and kinetin can retard postexcision senescent changes in the leaf, yielding protoplasts which are more resistant to spontaneous lysis and more active in protein and nucleic acid synthesis (9). Subsequently, the basic amino acids L-arginine and L-lysine were found to have similar effects, some of which are described here. rapid metabolism of these two amino acids to diamines occurring naturally in plant tissues (16), the ability of diamines to stabilize bacterial protoplasts against Iysis (19), and their involvement in nucleic acid synthesis in many procaryotic and eucaryotic organisms (18) including some plants (1, 8, 16), we studied the effects of various amines and related substances on macromolecular synthesis and morp...

“…In the darkened oat leaf proteolysis begins within 6 h and polysaccharide breakdown soon follows (25). The increased activity of ribonuclease in leaves of several species was also an early observation (9,28,34) although in oat leaves the rise in RNase was only transient (25,35). The RNase may be liberated only from bound form, but it may be actually synthesized.…”

mentioning

confidence: 99%

Metabolism of Oat Leaves during Senescence

Malik¹,

Thimann²

1980

The ATP content of 7-day-old A vena sativa leaves during senescence in dark and in light, and after treatment with cytokinins and other reagents, has been determined by the luciferin-luciferase method. Special care was taken to avoid decomposition of the ATP, and a detailed procedure is presented for ATP analysis at the picomole level. Preliminary experiments with several inhibitors of photophosphorylation suggest, though not conclusively, that the delaying effect of light on senescence is mediated by photophosphorylation. The ATP values of the leaves senescing in darkness are found to increase in parallel with the large increase in respiratory rate, and kinetin prevents this increase just as completely as it prevents the respiratory rise. It is concluded that the respiratory increase in senescence cannot be simply due to uncoupling. In light the ATP level also rises, though more slowly, and again kinetin prevents this rise. L-Serine, which promotes dark senescence, does not significantly modify the dark ATP level, but both arginine and kinetin, which antagonize the action of serine on senescence, greatly lower the ATP level below that on serine alone. Cycloheximide has a similar effect, and the combination of cycloheximide and kinetin lowers the ATP level drastically. Fusicoccin, which opens stomata in the dark, correspondingly maintains the ATP at a low level. Thus, in general, a low level of ATP is associated with the prevention of dark senescence, ie. probably with ATP utilization, and the ATP level at any time may thus be determined more by the rate of utilization than by the efficiency of respiratory coupling.It is well understood that leaf senescence is dominated by hydrolytic processes. In the darkened oat leaf proteolysis begins within 6 h and polysaccharide breakdown soon follows (25). The increased activity of ribonuclease in leaves of several species was also an early observation (9,28,34) These and other observations could be taken to indicate some relationship between leaf senescence and the products of phosphorylation. It was not clear whether oxidative phosphorylation in the dark and photophosphorylation in the light act in the same way, nor was it at all clear just what the nature of the postulated relationship actually is. As a first step toward clarification of these difficult questions, it was felt essential to determine the levels of ATP during senescence in both darkness and light and to follow the effects on leaf ATP of some of the agents and treatments that modify the senescence process. This paper reports those determinations. A preliminary study has also been made of several inhibitors of photophosphorylation to see whether they modify senescence in light. Two of these inhibitors do in fact interfere with the light effect on senescence and thus the results give general support to the idea that phosphorylation exerts a controlling influence on senescence. MATERIALS AND METHODSA survey of the literature showed that for small samples of plant material the luciferin-luciferase meth...