Abstract
Opuntia plants grow naturally in areas where temperatures are extreme and highly variable in the day during the entire year. These plants survive through different adaptations to respond to adverse environmental conditions. Despite this capability, it is unknown how CAM photosynthetic activity and growth in Opuntia plantlets is affected by constant heat or cold. Therefore, the main objective of this research was to evaluate the short-term effect of high (40°C) and low (4°C) continuous temperatures on the photosynthetic efficiency, the organic acid content (malic acid) and the relative growth rate (RGR) in seven-month-old Opuntia streptacantha plantlets during 5, 10, and 15 days. Chlorophyll fluorescence analysis allowed us to determine that high temperatures negatively impact the photosynthetic efficiency of O. streptacantha plantlets, which exhibited the lowest values of maximum quantum efficiency of the photosystem II (Fv/Fm = 52%, Fv/F0 = 85%), operational quantum yield of PS (ΦPSII = 65%) and relative electron transport rate (rETR = 65%), as well as highest values of basal fluorescence (F0 = 226%) during 15 days of treatment. Similarly, low temperatures decreased Fv/Fm (16%), Fv/F0 (50%), ΦPSII and rETR (16%). High temperatures also decreased nocturnal acidification in approximately 34–50%, whereas low temperatures increased it by 30–36%. Additionally, both continuous temperatures affected drastically diurnal consumption of malic acid, which was related to a significant RGR inhibition, where the specific photosynthetic structure area component was the most affected. Our results allowed determining that, despite the high tolerance to extreme temperatures described for Opuntia plants, young individuals of O. streptacantha suffered photosynthetic impairment that led to the inhibition of their growth. Thus, the main findings reported in this study can help to predict the potential impact of climatic change on the establishment and survival of succulent species of arid and semiarid regions of Mexico.
Highlights
Over the past 100 years, the global average temperature has changed and it is projected to continue changing at a rapid rate [1]
The photosynthesis status of O. streptacantha exposed to extreme temperatures (40 ̊C and 4 ̊C) was determined through the use of different parameters of chlorophyll fluorescence, as follows: the maximum quantum efficiency of the photosystem II (Fv/Fm), its more sensitive indicator of changes in the rates of photosynthetic quantum conversion, the (Fv/F0) [23], operational efficiency of the photosystem II (FPSII), basal or minimum fluorescence (F0), and relative Electron Transfer Rate after 5, 10, and 15 days
This study showed that the heat and cold stress had a clear impact on the photosynthetic activity of PSII, the nocturnal accumulation of organic acids and the diurnal consumption of malic acid, indicating an early impairment of photosynthesis and inhibition of growth in O. streptacantha plantlets
Summary
Over the past 100 years, the global average temperature has changed and it is projected to continue changing at a rapid rate [1]. Biochemical changes such as alterations in the viscosity, permeability and fluidity of the cell membrane are produced [3] and, at the enzymatic level, studies have reported changes or inhibition of Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), phosphoenol pyruvate carboxylase (PEP-case), pyruvate phosphate dikinase (PPDK), adenosine triphosphate (ATP) synthase, antioxidant enzymes, among others [3,4]. Most plants slow their growth at temperatures above 40 ̊C and under 10 ̊C mainly due to a reduction or inhibition of photosynthesis [5,6]. Nocturnal accumulation of malic acid and its daily variations can be estimated by titratable acidity, which allow to determine changes in CAM activity and carbon assimilation [11], especially when plants are subjected to environments where temperatures are extreme and highly variable during the day
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
