Plants under Climatic Stress

178

Severe photoinactivation of catalase (EC 1.11.1.6) and a decline of variable fluorescence (FJ), indicating photoinhibition of photosynthesis, were observed as rapid and specific symptoms in leaves exposed to a high heat-shock temperature of 40°C as well as in leaves exposed to low chilling temperatures in white light of only moderately high photosynthetic photon flux density of 520 ME m-2 s-'. Other parameters, such as peroxidase (EC 1.11.1.7), glycolate oxidase (EC 1.1.3.1), glutathione reductase (EC 1.6.4.2), or the chlorophyll content, were hardly affected under these conditions. At a compatible temperature of 22°C, the applied light intensity did not induce severe photoinactivations. In darkness, exposures to high or low temperatures did not affect catalase levels. Also, decline of F, in light was not related to temperature sensitivity in darkness. The effective low-temperature ranges inducing photoinactivation of catalase differed significantly for chilling-tolerant and chilling-sensitive plants. In leaves of rye (Secale cereale L.) and pea (Pisum sativum L.), photoinactivation occurred only below 15°C, whereas inactivation occurred at 15°C in cucumber (Cucumis sativus L.) and maize (Zea mays L.). The behavior of F, was similar, but the difference between chilling-sensitive and chillingtolerant plants was less striking. Whereas the catalase polypeptide, although photoinactivated, was not cleaved at 0 to 4°C, the Dl protein of photosystem 11 was greatly degraded during the lowtemperature treatment of rye leaves in light. Rye leaves did not exhibit symptoms of any major general photodamage, even when they were totally depleted of catalase after photoinactivation at 0 to 4°C, and catalase recovered rapidly at normal temperature. In cucumber leaves, the decline of catalase after exposures to bright light at 0 to 4°C was accompanied by bleaching of chlorophyll, and the recovery observed at 25°C was slow and required several days. Similar to the Dl protein of photosystem 11, catalase differs greatly from other proteins by its inactivation and high turnover in light. Inasmuch as catalase and Di protein levels depend on continuous repair synthesis, preferential and rapid declines are generally to be expected in light whenever translation is suppressed by stress actions, such as heat or chilling, and recovery will reflect the repair capacity of the plants.

Section: Discussionsupporting

confidence: 72%

Photoinactivation of Catalase Occurs under Both High- and Low-Temperature Stress Conditions and Accompanies Photoinhibition of Photosystem II

Feierabend¹,

Schaan²,

Hertwig³

1992

178

“…The rate of net photosynthesis in P. maximum has been shown to drop significantly when the plants are grown at temperatures below 25 C (22). Taylor et al (19) have proposed that pyruvate Pi-dikinase may be an enzyme which, through its cold sensitivity, regulates the temperature response of photosynthesis in C4-type plants. Pyruvate Pi-dikinase, however, has not been proposed to play a major role in photosynthesis in C4 plants such as P. maximum (3).…”

Section: Discussionmentioning

confidence: 99%

“…The generally low activity of PEPCK in both the carboxylating and decarboxylating direction at temperatures below 25 C suggest that PEPCK may be a cold-sensitive enzyme. Cold sensitivity of photosynthesis in C4 type plants is a well documented phenomenon (8,19,22). The rate of net photosynthesis in P. maximum has been shown to drop significantly when the plants are grown at temperatures below 25 C (22).…”

Section: Discussionmentioning

confidence: 99%

Characterization of Phosphoenolpyruvate Carboxykinase from Panicum maximum

Ray¹,

Black²

1976

PEPCK has been characterized from several microorganisms and animals (1, 5-7, 9). However, only limited information is available on the characteristics of this enzyme in higher plants and most of this has been obtained using crude extracts (2, 10-14, 16, 18). In addition, the data on plant PEPCK are on either the exchange reaction or the ADP-dependent carboxylation reaction. Using either of these reactions to study PEPCK in relation to C4 photosynthesis is open to criticism since the proposed role of PEPCK is as a decarboxylase. The exchange reaction has been found to occur at rates much faster (3-to 30-fold) than either the carboxylation or decarboxylation reaction in animal tissue (7) Even though PEPCK is proposed as the decarboxylase in bundle sheath cells of certain C4 plants, no information is available on the characteristics of the ATP-dependent decarboxylation of OAA by the enzyme (12)(13)(14). This report presents data on the partial purification of PEPCK to remove PEP carboxylase using the C4 grass Panicum maxinum. The ATP-dependent decarboxylation reaction has been characterized and compared to the exchange reaction and the ADP-dependent carboxylation reaction.Phosphoenolpyruvate carboxykinase catalyzes the nucleotidedependent carboxylation of PEP2 to produce OAA in a reversible fashion as shown in equation 1. CO2 + ADP + PEP+&I% +OAA + ATP (1) In addition, PEPCK catalyzes a nucleotide-dependent exchange of CO2 into OAA (16,20).PEPCK has been proposed to act as a decarboxylase during photosynthesis in bundle sheath cells of specific plants which carry out C4 photosynthesis such as Panicum maximum. Through the action of PEPCK in these C4 plants, CO2 is released from OAA in the bundle sheath cells where the CO2 is refixed by the C3 cycle (3,12,14). In other C4 plants either a NADP+-or NAD+-dependent malic enzyme acts as the decarboxylase in bundle sheath cells. In all C4 plants the 4-carbon organic acids 1

“…A significant level of ATPase activity was detected in the region between the activity peaks of the tonoplast and the plasma membrane ATPases, i.e., fractions 15 to 18, where the Golgi membranes cofractionated. The activity in these fractions was significantly lowered upon chilling for 1 d and further declined with (21,25), although it is sometimes difficult to determine whether such impairments are the result or the cause of cell injury. In mung bean hypocotyls, electrolyte leakage from cells after rewarming cannot be the cause of injury, but is probably the result of a secondary-induced cellular event.…”

Section: Changes In Density Gradient Profiles Of Cellular Membranesmentioning

confidence: 99%

Impairment of Tonoplast H⁺-ATPase as an Initial Physiological Response of Cells to Chilling in Mung Bean (Vigna radiata [L.] Wilczek)

Yoshida

Matsuura²,

Etani³

1989

Biochemical alterations of cellular membranes in chilling-sensitive mung bean (Vigna radiata [L.] Wilczek) hypocotyls were invesfigated with reference to chilling injury. Reversible decreases in activities of tonoplast H+-ATPase and in vivo respiration became manifest within 24 hours of chilling when tissues suffered no permanent injury as assessed by electrolyte leakage and regrowth capacity. These changes were found to be the earliest cellular responses to chilling. A density-shift on a sucrose density gradient was observed in Golgi membranes early in the chilling treatment, suggesting that Golgi function and/or membrane biogenesis via the Golgi may have been altered upon chilling. After chilling more than 2 days, irreversible changes were generally produced in cellular membranes including the plasma membrane, endoplasmic reticulum, and mitochondria. Respiratory functions remained intact in mitochondria isolated from tissues prechilled for 24 hours, but were impaired after prechilling for 3 days. Given the important role of the tonoplast H+-ATPase in the active transport of ions and metabolites, the early decline in the tonoplast H+-ATPase activity may give rise to an alteration of the cytoplasmic environment and, consequently, trigger a series of degenerative reactions in the cells. uncertainty as to how the chill-induced physical changes in those membranes can be sequentially transduced into cell injury. Furthermore, there seems to be no specific reason to assume that those organelles are exclusive cellular sites for sensing low temperatures.In our earlier studies, using extremely chill-sensitive cultured cells (27), degeneration ofcell structures occurred within a short period of chilling, i.e., 6 to 12 h at 0°C. Partial dilation and microvesiculation of RER and other deteriorative changes were followed by marked morphological changes in the intramembranous particles on the tonoplast fracture faces. Furthermore, the chilled cells retained the capacity to grow after transfer to a warm temperature until the onset of the structural alteration in the tonoplast. It is assumed that chillinduced structural and functional deterioration in the tonoplasts is also involved in the earliest cellular events triggered by chilling. In the present study, we have attempted to analyze the biochemical changes in various cellular membranes, which take place during chilling in the cells in chill-sensitive mung bean seedlings. Special attention was paid to determining the earliest changes manifested in intact cells immediately upon chilling and to distinguish them from the secondarily transduced ones.Although a number of studies have been carried out to elucidate the mechanisms involved in chilling injury in plants, many problems remain to be explained. For a better understanding of the mechanisms, it is important to identify the cellular site(s) and the physical features of the primary reaction(s) sensing low temperatures and to determine the physiological transducers transmitted from the low temperature sensing reaction...