New instrumentation in grapevine research: A dual respiration prototype for grape berries and whole bunch. The grape CO2/O2 respiratory quotient revisited

Abstract

Grape berry respiration is a key process during maturation, since it influences must acidity. In recent literature, there are some reports showing measurements of bunch respiration, as CO2 efflux, from the point of view of the plant C balance. Traditionally, in the late 60 s and 70 s, grape berry respiration, either as CO2 or O2, was measured by slicing grape berries and using the standard Warburg method. Commercially available instruments adequate to measure gas exchange, particularly H2O (transpiration) and CO2 (respiration or photosynthesis), in small fruits (typically apples) are not suitable for a whole bunch or isolated grape berries.In this report, we present a low-cost, closed chamber system where the gases (CO2 and O2) are allowed to accumulate/be consumed, based on the use of sensors from Vaisala (CO2) and SST Sensing (O2), which can monitor respiration in a whole bunch of grape berries, or alternatively in isolated grape berries.Respiration was measured in whole Tempranillo bunches sampled at different phenological stages with the whole bunch respiration prototype. Results showed a decreasing trend of respiration from pea size to maturity (both measured as CO2 efflux and O2 uptake) with an almost constant CO2/O2 respiratory quotient of around 1.3. Data from the old literature postulated an increase in this respiratory quotient when grapes start to ripen. Since the measurement in a whole bunch modifies the relationship between the air volume circulating around the bunch as it grows in size with the phenological stage, we optimized the system by reducing as much as possible the air death volume using an alternative chamber for isolated grape berries. Measurements of Tempranillo grape berries collected at different phenological stages using this new closed system confirmed the decreased respiration trend throughout grape development and ripening period. Even most important, these respiration measurements resulted in a change of the CO2/O2 respiratory quotient from ca. 1.0 before veraison to 1.3 and 1.2 at veraison and maturity, respectively. These data suggest a change in the respired substrate from hexoses to organic acids, putatively mainly malic acid. Finally, a series of respiration measurements as CO2 efflux was made to check any possible physiological effect of cutting the bunch or the grape berry. A very important result of these series of measurements is that the fact of detaching the bunch from the plant or the grape from the bunch did not change the bunch/grape berry respiration rate, at least for several hours.