Freezing damage and frost tolerance of the photosynthetic apparatus studied with isolated mesophyll protoplasts of Valerianella locusta L.

Abstract

Mesophyll protoplasts were isolated from unhardened and cold-acclimated leaves of Valerianella locusta L. and subjected to freeze-thaw treatment. To evaluate the extent and course of freezing injury, photosynthetic reactions of whole protoplasts and of free thylakoid membranes, liberated from protoplasts by osmotic lysis, were measured. In addition, the integrity of the protoplasts was determined by microscopy. The results reveal an increased frost tolerance of protoplasts isolated from acclimated leaves with respect to all parameters measured. CO2-dependent O2 evolution (representing net photosynthetic CO2 fixation of protoplasts) was the most freezing-sensitive reaction; its inhibition due to freeze-thaw treatment of protoplasts was neither correlated with disintegration of the plasma membrane, nor was it initiated by inactivation of the thylakoid membranes. The frost-induced decline of protoplast integrity was not closely correlated to thylakoid damage either. Freezing injury of the thylakoid membranes was manifested by inhibition of photosynthetic electron transport and photophosphorylation. Both photosystems were affected by freezing and thawing with strongest inhibition occurring in the water-oxidation system or at the oxidizing site of photosystem II. Photophosphorylation responded more sensitively to freezing stress than electron transport, although uncoupling (increased permeability of the thylakoid membranes to protons) was not a conspicuous effect. The data are discussed in relation to freezing injury in leaves and seem to indicate that frost damage in vivo is initiated at multiple sites.

Understanding the cellular mechanism of recovery from freeze–thaw injury in spinach: possible role of aquaporins, heat shock proteins, dehydrin and antioxidant system

“…Thylakoid rupture and declined photosynthesis (e.g. inhibited photosynthetic electron transport and photophosphorylation) have also been observed in freeze–thaw stressed tissues (Rumich‐Bayer and Krause , Hincha et al , Steffen et al , Ehlert and Hincha ).…”

Relative Sensitivity of Photosynthesis and Respiration to Freeze-Thaw Stress in Herbaceous Species

“…In spite of these common observations, investigations into the mechanisms of frost tolerance frequently use very fast cooling rates, commonly 6 to 60°C/h (3,10,24,25). In addition, little attention is given to the point at which ice nucleation is initiated.…”

“…Levitt (1 1) noted (but provided no data) that air cooling rates in nature are usually less than 1 to 2°C/h and that ice nucleation generally occurs before tissue temperature reaches -2°C. In spite of this common observation, some recent studies investigating the mechanism of freezing injury have used cooling rates of 6 to 20°C/h (10,25) and 60°C/h (3,24). In some studies there is no indication that the nucleation temperature was controlled (9,10,25).…”

“…In spite of this common observation, some recent studies investigating the mechanism of freezing injury have used cooling rates of 6 to 20°C/h (10,25) and 60°C/h (3,24). In some studies there is no indication that the nucleation temperature was controlled (9,10,25). Many studies investigating the mechanism of freezing injury to the photosynthesis apparatus using isolated membrane preparations have utilized cooling rates of 20 to 1 50C/h (4,5,26).…”

Transcriptomic and Metabolomic Approaches to the Analysis of Plant Freezing Tolerance and Cold Acclimation

“…In herbaceous plants, acclimation is triggered by exposure to low, nonfreezing temperatures, usually in the range between 10 and 0 C over several days and increases the freezing tolerance in different species by approximately 2-25 C [4, 22,[24][25][26][27]. In woody species, photoperiod is an additional determinant of acclimation, with a combination of low temperature and short days inducing the highest freezing tolerance [28,29].…”