Abstract
Low temperature (LT) is an important abiotic factor affecting plant survival, growth and distribution. The response of Cryptomeria fortunei (Chinese cedar) to LT is not well known, limiting its application in production and ornamental value. In this study, we first screened ten clones (#3, #25, #32, #42, #54, #57, #68, #66, #74, #X1), originating from five different locations in China, for their degrees of cold resistance. We then selected the two showing the highest (#32) and lowest (#42) cold resistance to see the physiological and morphological response of different cold-resistant C. fortunei clones to LT. We found that the electrolyte leakage of all ten clones increased strongly between 0 and −8 °C, while below −8 or between 4 and 0 °C did not yield additional increases. Under cold stress, clones #32 and #42 showed different degrees of needle browning. From 25 to −20 °C, maximum and effective quantum yields of photosystem II (Fv/Fm and YII) and photochemical and non-photochemical quenching (qP and NPQ) decreased continuously in two clones with decreasing temperature, where #42 was more strongly affected compared with #32. The chlorophyll content first decreased significantly to the lowest from 25 to −12 °C, then increased significantly at −16/−20 °C compared with −12 °C. We observed changes in needle cellular ultrastructure at −8 °C, with chloroplasts of #32 swelling, while those of #42 were destroyed. Correlation analysis indicated that needle browning and chlorophyll fluorescence were closely related to temperature, and cellular ultrastructure changed notably around semi-lethal temperature (LT50), which can be used as physiological indicators for the identification of cold resistance. We found a clear difference in cold tolerance between clones of #32 and #42, with #32 being more tolerant, which can be exploited in breeding programs. We conclude that strongly cold-resistant clones have more stable physiological states and a wider adaptability to LT compared with weak ones.
Highlights
Low temperature (LT) is one of the most important abiotic stress factors affecting plant survival and growth, and it is the main factor that determines the geographical distribution and growth season of plants [1]
Since we found that increasing low-temperature stress (LTS) caused a greater degree of needle browning in C. fortunei, we sought to determine whether the chlorosis we observed was related to a decrease in chlorophyll content and low cold resistance
We found the LT50 of 10 tested clones of C. fortunei to be between −4.7 and −7.8 ◦ C, with #32 having the lowest value at −7.8 ◦ C and #42 the highest at −4.7 ◦ C, suggesting that #32 and #42 have the strongest and weakest cold resistances, respectively
Summary
Low temperature (LT) is one of the most important abiotic stress factors affecting plant survival and growth, and it is the main factor that determines the geographical distribution and growth season of plants [1]. Cold resistance is a complex feature and can be a major influence on plant survival [2]. During their life cycles, most terrestrial plants that are grown in temperate or cold regions are affected. Freezing stress usually leads to the formation of intracellular ice crystals, as well as mechanical dehydration, which will cause an increase of intracellular salt concentration, irreversible damage to plant cells and metabolic defects [4,5]. Frost-resistant plants are assumed to have specific cellular structures and intracellular components that are able to withstand the mechanical and osmotic stresses caused by freezing. Previous studies have shown that cold treatment on LT-sensitive plants accelerates their electrolyte flow and increases permeability of cellular membranes, leading to serious membrane damage and “membrane leakage” phenomena [7]
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