Physiological effects of temperature and growth regulators on foliar chlorophyll,soluble protein,and cold hardiness in citrus

Leaf chlorophyll (Chl, A, B) and total soluble protein were assayed in greenhouse-grown 1.5-year-old trees of 2 citrus types, trifoliate orange (Poncirus trifoliata (L.) Raf.) and sour orange (Citrus aurantium L.) exposed to 12 h (day/night) photoperiods in growth chambers under high (30°/21°C, day/night; noncold-hardening) and low (16°/5°C; cold-hardening) temperature regimes. Trees were sprayed 2 × per week for 5 weeks with one of the following solutions at 100 M: napthaleneacetic acid (NAA), paclobutrazol (2RS, 3RS)-1-(4-chlorophenyl-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol) (PPP333), benzyl-adenine (BA), abscisic acid (ABA), gibberellic acid (GA₃), minerals only (N, P, K, S, Ca, Mg) and BA (+) minerals. NAA, PP333, ABA and GA₃ decreased Chl A, B and soluble protein in both citrus types under cold-hardening conditions in contrast to increases with the use of BA and BA (+) minerals especially in trifoliate orange. Both BA and GA₃ increased Chl A, B and protein synthesis under high temperature in both citrus types. Under noncold-hardening temperatures, GA₃ enhanced Chl A, B but sharply reduced foliar protein concentration. Dieback of both cultivars following exposure to temperatures down to –6.7°C was decreased 7% by NAA sprays during noncold-hardening temperatures. Cold tolerance of noncoldhardened trifoliate orange trees was also improved with ABA and PP333. Foliar sprays of NAA (sour orange) and PP333 and BA (+) minerals (trifoliate) increased cold tolerance of cold-hardened trees by 8%. Results indicate that spray applications of growth regulators influence physiological factors associated with foliar functioning and cold tolerance in citrus during different temperature regimes.Summary Growth promoters (BA) and inhibitors (NAA) have the potential to promote cold hardines through either a strong stimulatory effect on foliar physiology or a marked inhibition of growth in general. This suggests that each growth regulator may possess an independent role in the cold-hardiness phenomenon and may also interact with physiological processes other than soluble protein and chlorophyll metabolism. The relationship between soluble protein levels in citrus foliage and the degree of cold hardiness remains uncertain and is essentially unresolved pending more specific qualitative research.University of Florida Agricultural Experiment Station Series No. 7446.This paper reports the results of research only. Mention of a trademark of a proprietary product does not constitute a recommendation for use by the U.S. Department of Agriculture to the exclusion of other products that may also be suitable.     

Metabolic correlates to glycerol biosynthesis in a freeze-avoiding insect,Epiblema scudderiana

Summary The course of glycerol biosynthesis, initiated by exposure to –4°C, was monitored in larvae of the goldenrod gall moth,Epiblema scudderiana, and accompanying changes in the levels of intermediates of glycolysis, adenylates, glycogen, glucose, fructose-2,6-bisphosphate, and fermentative end products were characterized. Production of cryoprotectant was initiated within 6 h after a switch from +16° to –4°C, with halfmaximal levels reached in 30 h and maximal content, 450–500 mol/g wet weight, achieved after 4 days. Changes in the levels of intermediates of the synthetic pathway within 2 h at –4°C indicated that the regulatory sites involved glycogen phosphorylase, phosphofructokinase, and glycerol-3-phosphatase. A rapid increase in fructose-2,6-bisphosphate, an activator of phosphofructokinase and inhibitor of fructose-1,6-bisphosphatase, appeared to have a role in maintaining flux in the direction of glycerol biosynthesis. Analysis of metabolite changes as glycerol production slowed suggested that the inhibitory restriction of the regulatory enzymes was slightly out of phase. Inhibition at the glycerol-3-phosphatase locus apparently occurred first and resulted in a build-up of glycolytic intermediates and an overflow accumulation of glucose. Glucose inhibition of phosphorylase, stimulating the conversion of the activea to the inactiveb forms, appears to be the mechanism that shuts off phosphorylase function, counteracting the effects of low temperature that are the basis of the initial enzyme activation. Equivalent experiments carried out under a nitrogen gas atmosphere suggested that the metabolic make-up of the larvae in autumn is one that obligately routes carbohydrate flux through the hexose monophosphate shunt. The consequence of this is that fermentative ATP production during anoxia is linked to the accumulation of large amounts of glycerol as the only means of maintaining redox balance.Abbreviations G6P glucose-6-phosphate - F6P fructose-6-phosphate - F1, 6P fructose-1,6-bisphosphate - F2,6P ₂ fructose-2,6-bisphosphate - G3P grycerol-3-phosphate - DHAP dinydroxyacetonephosphate - GAP glyceraldehyde-3-phosphate - PEP phosphoenolpyruvate - PFK phosphofructokinase - FBPase fructose-1,6-bisphosphatase - PK pyruvate kinase     

Total nitrogen and free amino acids in Morus alba stems from autumn through spring

During leaf senescence and abscission, total nitrogen in leaves of mulberry ( Morus alba L. ev. Shin-ichinose) declined substantially whereas total nitrogen in buds, bark and stem wood increased markedly, suggesting translocation of nitrogen from senescent leaves in the autumn. After leaf abscission the winter buds and stems remained almost unchanged with respect to fresh and dry weight and total nitrogen until bud break in spring. In burst buds these parameters then increased drastically during the new growth while they decreased markedly in stems. Free arginine in the stem bark accumulated in parallel with the accumulation of total nitrogen in buds and stems in the autumn. Accumulation of proline in the wood, bark and buds also started in October but continued even after leaf-fall, increasing until mid-January (wood), mid-February (bark) and the new growth (buds). Prior to and in the early stage of bud break, proline in bark and wood decreased significantly and arginine in stem bark decreased slightly. Simultaneously, proline and arginine in the dormancy-releasing buds and asparagine, aspartic acid and glutamic acid in the buds and stems increased appreciably, suggesting that this increase in free amino acids was mainly derived from free amino acids (proline and arginine) stored in stems. The resulting marked decrease in total nitrogen and the drastic increase in asparagine in the stems and sprouting buds/new shoots were primarily due to a breakdown of protein stored in stems.     

Further studies on the involvement of the circadian system in photoperiodic control of antifreeze protein production in the beetle Dendroides canadensis

The role of circadian rhythmicity in the photoperiodic time measuring processes regulating antifreeze protein production in the beetle Dendroides canadensis was further investigated. Using “T” experiments larvae were exposed to environmental light cycle periods close to the period length of the endogenous circadian oscillator. The following light cycles were employed: light/dark 8/13, 8/14, 8/16, 8/18 and 8/19 corresponding to period lengths of 21, 22, 24, 26 and 27 h. Larvae maintained in cycles equal to or less than 24 h displayed a characteristic short-day response, showing significantly (P < 0.01) greater antifreeze protein activity than did those measured on the day of collection in late summer. In contrast, a long-day response was observed in larvae maintained under a 26- or 27-h light cycle in that antifreeze protein activity did not differ from that measured on the initial collection date.

The role of photoperiod and temperature in influencing the photoperiodic timing processes were examined with a series of resonance experiments. The first group consisted of a 24, 36, 48, 60 or 72-h light cycle, each with an 8-h photophase at temperatures of 20 or 17°C. Rhythmic increases in antifreeze protein levels at intervals of 24 h occurred under both temperatures. However, the lower temperature displaced the resonance curve in the vertical direction (i.e. increasing % population response) and reduced the difference between peaks and troughs on the resonance curve. Resonance experiments incorporating a 14-h photophase resulted in low antifreeze protein activity under all conditions except a 36-h light cycle in which a 67% induction was observed.

Eight hour resonance experiments were also conducted with D. canadensis collected in early spring to determine whether the circadian system participates in the photoperiodic timing processes influencing the spring termination of antifreeze protein production. Positive resonance results were obtained in that only larvae maintained in cycles of 36 and 60 h displayed significantly (P < 0.01) lower antifreeze activity when compared to animals on the initial collection date.

The combined results emphasize the involvement of the circadian system in the photoperiodic control of antifreeze protein production by D. canadensis during the fall and spring. Furthermore, the induction of antifreeze protein production is a function of light cycle and its waveform (photoperiod). Temperature appears to modify the photoperiodic response in some manner involving the photoperiodic time measuring processes. It is concluded that the photoperiodic response of antifreeze protein production by D. canadensis is dependent upon the entrainment of the circadian system by the light cycle.     

Climate and plant distribution at global and local scales

This paper investigates, with predictive models, the utility of ecophysiological responses to climate as predictors of plant distribution. At the global scale responses to extreme minimum temperatures and to the hydrological budget effectively predict the distribution limits of the major vegetation types of the World. A minimum temperature of -15°C, for example, appears critical in controlling the poleward spread of vegetation that is dominated by evergreen broadleaved species; however, the presence or absence of more frost resistant species, such as those that are deciduous broadleaved, is not obviously explained in terms of extremes of climate. In such cases, predicting the competitive relationships between species is necessary and dependent on the climatic sensitivity of population dynamics.We are grateful to Hans de Kroon for discussions on the application of matrices to ecology.     

微管的冷稳定性与植物抗寒性关系的研究

利用间接免疫荧光的细胞化学技术对番茄、黄瓜、菠菜、甜菜及小麦等不同抗寒性植物微管的冷稳性进行了比较研究。结果指出,不抗寒的喜温性植物番茄和黄瓜的气孔保卫细胞的微管在0℃—1℃冷处理3小时即解聚;属于中等抗寒性植物的菠菜和甜菜幼苗经秋季低温锻炼后,其气孔保卫细胞的微管在0℃和—5℃低温处理3小时,均不发生解聚;具有较强抗寒性的冬小麦品种农大139幼苗在2—3℃低温锻炼期间,微管结构保持完整,经过15天低温锻炼的幼苗在-8℃冰冻处理3小时,微管也不受破坏。这些结果表明,微管的冷稳性与植物的抗寒性成正相关。     

Changes in parameters of the plasmalemma ATPase during cold acclimation of apple (Mains domestica) tree bark tissues

A plasmalemma fraction was isolated from homogenized apple tree (Mains domestica Borkh 'Golden Delicious') hark tissues using aqueous phase partitioning and ultra-centrifugation. Results of marker enzyme assays indicated that a membrane preparation highly enriched in plasma membranes was obtained. ATPase activity in this preparation possessed a high specificity for ATP as substrate, was inhibited by vanadate, diethylstilbcsterol and dicyclohexylcarbocHimide, and was insensitive to inhibitors of mitochondria! and tonoplasl ATPases. Specific activity of the plasma-lemma ATPase increased during cold acclimation prior to the attainment of vegetative maturity. Kinetic parameters (Km, Vln) determined from assays performed at different temperatures (10, 30°C) indicated a differential effect of cold acclimation on enzyme activity. Vm increased during cold acclimation, whereas Km increased when determined at 30°C but declined at 10°C. Acclimation treatments during April and May resulted in alteration of ATPase kinetics in the absence of any increase in bark frost hardiness. Changes in ATPase kinetics may be related more to enhanced low temperature metabolism than to frost hardiness per se.     

Cold hardiness and water relations parameters in Rhododendron cv. Catawbiense Boursault subjected to drought episodes

We determined whether increase in cold hardiness of Rhododendron cv. Catawbiense Boursault induced by water stress was correlated with changes in tissue water relations. Water content of the growing medium was either maintained near field capacity for the duration of the study or plants were subjected to drought episodes at different times between 15 July and 19 February. Watering during a drought episode was delayed until soil water content decreased below 0.4 m³ m⁻³ then watering was resumed at a level to maintain soil water content between 0.3 and 0.4 m³ m⁻³. Cold hardiness was evaluated in the laboratory with freeze tolerance tests on detached leaves. Water relations parameters were determined using pressure-volume analysis. Exposure to drought episodes increased cold hardiness during the cold acclimation stage in late summer and fall but not during the winter. When water-stressed plants were re-watered to field capacity, the previous gain in cold hardiness gradually disappeared. Water relations parameters correlating with seasonal changes of cold hardiness included dry matter content (r =−0.67). apoplastic water content (r =−0.60), and water potential at the turgor loss point (r = 0.40). Changes of cold hardiness in water-stressed plants in reference to well-watered plants were correlated with changes of all water relations parameters, except for osmotic potential at full turgor (r = 0.13). It is proposed that water stress reduced the hydration of cell walls, thereby increasing their rigidity. Increased rigidity of cell walls could result in a development of greater negative turgor pressures at subfreezing temperatures and therefore increased resistance to freeze dehydration.     

Cold acclimation and photoinhibition of photosynthesis in Scots pine

Cold acclimation of Scots pine did not affect the susceptibility of photosynthesis to photoinhibition. Cold acclimation did however cause a suppression of the rate of CO₂ uptake, and at given light and temperature conditions a larger fraction of the photosystem II reaction centres were closed in cold-acclimated than in nonacclimated pine. Therefore, when assayed at the level of photosystem II reaction centres, i.e. in relation to the degree of photosystem closure, cold acclimation caused a significant increase in resistance to photoinhibition; at given levels of photosystem II closure the resistance to photoinhibition was higher after cold acclimation. This was particularly evident in measurements at 20° C. The amounts and activities of the majority of analyzed active oxygen scavengers were higher after cold acclimation. We suggest that this increase in protective enzymes and compounds, particularly Superoxide dismutase, ascorbate peroxidase, glutathione reductase and ascorbate of the chloroplasts, enables Scots pine to avoid excessive photoinhibition of photosynthesis despite partial suppression of photosynthesis upon cold acclimation. An increased capacity for light-induced de-epoxidation of violaxanthin to zeaxanthin upon cold acclimation may also be of significance.Abbreviations APX ascorbate peroxidase - DHA dehydroascorbate - DHAR dehydroascorbate reductase - Fm maximal fluorescence when all reaction centres are closed - Fv/Fm maximum photochemical yield of PSII - GR glutathione reductase - GSH reduced glutathione - Je rate of photosynthetic electron transport - MDAR monodehydroascorbate reductase - q_N nonphotochemical quenching of fluorescence - q_P photochemical quenching of fluorescence - SOD superoxide dismutase This work was supported by the Swedish Natural Science Research Council and the National Natural Science Foundation of China.