No description available.

No description available.

Leaves of tropical and sub-tropical species are rapidly chill-injured when exposed to temperatures in the 0 to 10°C range. In contrast, leaves of temperate and arctic alpine species can withstand these temperatures without damage. Chill-sensitive leaves can be divided into two categories based on their susceptibility to chilling-injury:- 1) Extremely chill-sensitive species which are rapidly damaged on exposure to temperatures between 12 to 15°C (e. g. Episcia reptans) and which cannot be readily hardened against chilling-injury. Maintaining 100 per cent relative humidity during chilling at 5°C does not prevent injury to these species, although the speed at which injury occurs is reduced. 2) Chill-sensitive species which are damaged in the 0 to 10°C range (e. g. Phaseolus vulgaris) and which can be readily hardened against chilling-injury at 5°C, 85 per cent RH, by 4 days growth at 12°C, 95 per cent RH, before chilling. Maintaining 100 per cent RH during t chilling at 5°C prevents injury to these species. It is considered that the primary response in chilling-injury is a temperature induced phase transition in the lipids of the cellular membranes from a liquid-crystalline to a solid gel state. The temperature at which the phase change occurs appears to be determined mainly by the degree of unsaturation of the fatty-acids associated with the phospholipids. The chill-sensitivity of leaves grown at 25&°C was related to a low percentage of linoleic and linolenic acid associated with each phospholipid. The degree of unsaturation of the glycolipids could not be related to, the chill-sensitivity of the species. Hardening the chill-sensitive species Phaseolus vulgaris and Gossypium hirsutum against chilling-injury at 5°C, 85 per cent RH, resulted in increases of up to 12 per cent in the percentage of linoleic acid associated with all the leaf phospholipids. The degree of unsaturation of the glycolipids did not change during hardening. The increases in unsaturation of the phospholipids were shown to be positively related to the increased tolerance of the plants to chilling by the fact that similar increases did not occur during the growth of chill-resistant Hordeum vulgare at 12°C and the ineffective attempts at hardening chill-sensitive Episcia reptans over 4 days at 15°C, the lowest temperature this species can withstand without injury. Chilling-injury in Phaseolus vulgaris could be prevented by enclosing the plants in polythene bags at 5°C, thus maintaining 100 per cent RH. However, leaves of this species transferred from 25°C to 5°C. 100 per cent RH and 12°C, 100 per cent RH for 4 days did not harden against subsequent chilling-injury at 5°C 85 per cent RH. In agreement with this finding no increase in unsaturation of the phospholipids was detected over 4 days growth at 5°C 100 per cent RH, and 12°C 100 per cent RH. It is suggested that plants grown at 5 and 12°C 100 per cent RH, by enclosure in polythene bags do not harden against subsequent chilling- injury at 5°C 85 per cent RH, because the carbon dioxide concentration within the bag is rapidly lowered by photosynthetic fixation. This results in the cessation of photosynthesis and a reduced supply of the cofactors oxygen and NADPH available for desaturase activity, thereby preventing an increase in the degree of unsaturation of the phospholipids. An increase in leaf age at 25°C was shown to increase the susceptibility of chill-sensitive plants to chilling-injury. This increase in susceptibility of older leaves to damage was related to a decrease in the degree of unsaturation and weight of phospholipids with increase in physiological age at 25°C. In conclusion, the results reported in this investigation provide evidence that hardening chill-sensitive leaves prevents chilling-injury by increasing the degree of unsaturation of the membrane phospholipids thereby lowering the transition temperature of the lipid layer of the cellular membranes. This phase change does not occur on chilling chill-resistant plants but may occur at sub-zero temperatures and increase their susceptibility to freezing-injury.

A comparative study of the carbohydrate metabolism of roots of pea (Pisum sativum var. meteor) and maize (Zea mays var kelvedon glory) seedlings was undertaken at low temperatures (2-14°C) with the aim of demonstrating differences between these species which may be associated with the differing growth capacities of their roots mot this temperature range. Pea roots displayed linear growth rates at all temperatures tested whereas maize roots ceased growth over five days at temperatures below 6°C At the respective temperatures which were minimal for root growth of the two species, roots behaved similarly with regards to soluble sugar content; firstly, total content was maintained in the roots at the initial level, and secondly, sucrose content was at its highest value and glucose content at its lowest. With rise in temperature sucrose content declined while glucose content increased. In maize roots kept at those temperatures where growth was not sustained this relationship broke down. Total sugar content of the roots was not maintained, glucose content was abnormally high and sucrose content very low. Similarly, respiration rate of maize roots at 2°C was abnormally low. When seedings were grown with roots bathed in an external solution of glucose at 2°C (or of glucose or of sucrose at 6°C the disturbances to sugar metabolism and respiration rate of maize roots were partially alleviated and this was associated with a greater amount of growth made by the roots. Examination of the activity and Km of acid invertase extracted from the roots and partially purified, showed that the sucrose levels in roots of both species were inversely related to invertase activity. However in pea, but not in maize roots, Km values for invertase showed a lowering in value after growth of seedlings at 2°C compared with 20°C. Furthermore, in pea, after growth of seedlings at 14 or 2°C Km determined at 2°C was significantly lower than when determined at 14°C. These properties are of adaptive significance at low temperatures since they will act to maintain an appreciable reaction rate. Shifts in Km of a homeostatic nature with respect to temperature were not recorded for invertase from maize roots and in this species the failure to control invertase activity at low temperatures with consequent depletion of sucrose may be associated with the inability of this species to show sustained growth at 2°C. Examination of the Km of MDH likewise revealed a shift in Km value tending to buffer the effect of temperature on reaction rate for MDH from pea but not from maize roots.

Factors affecting the survival of over-wintering tree roots during waterlogging were investigated. Die-back of roots covered by high Winter water tables results in shallow rooted trees susceptible to wind-throw. Such is the scale of the problem in Britain, this research is considered to be of practical relevance. Sitka spruce (Picea sitchensis (Bong.) Carr.) and Lodgepole pine (Pinus contorta Douglas ex Loudon) were chosen, being the most predominant species planted and showing differing susceptibility to flooding. Sitka spruce is considered flood-intolerant (Crawford 1982) and Lodgepole pine highly-tolerant (Minore 1968). In both species, waterlogging the whole root system for 3 months severely reduced the carbohydrate content of the distal 15cm root, reflecting almost total depletion of starch reserve and varying degrees of glucose depletion. In Sitka spruce, depletion depended on the date of flood-initiation, being most severe after flooding from October when root respiration rate was higher, rather than November as the roots became dormant. Flooding injury was reflected in decreased tri-phenyl tetrazolium chloride reduction and loss of respiratory capacity. Greater loss of aerobic (as compared to anaerobic) respiration capacity after flooding suggested damage to the aerobic pathway, either directly through anoxia or indirectly due to depletion of sugars important in cell maintenance. Injury appeared to be greater when respiratory activity at flood-initiation was high. Aeration from stem lenticels ameliorated flood-injury and carbohydrate depletion in Lodgepole pine, although the roots appeared to have no metabolic adaptation to anoxia. Increased soil temperature during Winter flooding increased carbohydrate depletion in the distal root and reduced viability relative to seedlings flooded at ambient temperature. Carbohydrate depletion during cold storage and its effect on survival of soil waterlogging at out-planting was determined in Sitka spruce. Cold storage leads to increased root growth and slightly superior flood-tolerance when compared to nursery over-wintered seedlings, presumably due to the more dormant state of stored seedlings.

No description available.

Call number: LD2668 .T4 1952 P38 / Master of Science

Call number: LD2668 .T4 1959 Z43

In 1984 and 1985 visual differences in frost damage were observed among 40 jojoba clones growing in a field in Tucson, Arizona. More detailed data were collected on the clone with the least damage (Clone-1) and the one with the most damage (Clone-2). On 10-ten terminal branch samples, Clone-1 showed an average of 12% leaf damage compared to 35% for Clone-2. Leaf freezing under controlled conditions on a monthly schedule showed that leaves of Clone-1 consistently froze at a lower temperature than Clone-2. Also, a second exotherm occurred in 50% of the samples for Clone-1 whereas a second exotherm occurred in only 15% of the samples of Clone-2. Soil moisture content and plant water potential were measured biweekly. Neither seemed to relate to the differences in freezing tolerance of the two clones. Total nonstructural carbohydrates (TNC), total soluble sugars, sucrose and proline were determined monthly. Accumulation patterns of TNC were similar for the two clones, however, Clone-1 generally accumulated more soluble sugars, sucrose and proline which might have contributed to its freezing tolerance. Growth measurements were recorded monthly to determine whether differences occurred between the two clones. Growth of both clones peaked in the spring, showed minor peaks in summer and ceased in winter. Under greenhouse conditions, pot grown cuttings from Clone-1 and Clone-2 were given zero, six or 12 gm of Osmocote fertilizer and watered at 35 or 70% field capacity to determine the effect of irrigation and fertilization on leaf freezing point. Fertilization significantly increased leaf concentrations of N and P and produced more growth. In the greenhouse study, no differences were found in leaf freezing point due to clones, irrigation or fertilization treatment. Leaves of Clone-1 froze at a higher temperature compared to field grown plants.

No description available.