Abstract:
Dormancy of 'Pinot Noir' grapevines was characterized. Primary buds
required ca 300 cumulative chilling hours (CCH) to initiate the transition from
endodormancy to ecodormancy, which occurred in mid November. Additional
chilling, up to 1000 CCH, improved budbreak. Changes in bud water content
were estimated by gravimetric and spectroscopic methods. Total, intra-, and
extracellular water were measured gravimetrically. The total water and the
intracellular fraction increased during the ecodormant period.
A method to evaluate bud water status by proton-nuclear magnetic
resonance was developed. Grape buds present anisotropic behavior. Using this
method, water content was partitioned into free and bound fractions. Free water
was always larger than bound water. Furthermore, bound water reached its peak
in January when ecodormant plants were exposed to colder temperatures. These
results support former evidence that bound water is composed of one population
with restricted mobility, and another in a transient state.
Respiration pattern of overwintering buds was investigated using
differential scanning calorimetry. Endodormant buds decreased their respiration.
In February, an increase in respiration, typical of the period preceding budbreak,
was observed in ecodormant buds. Ecodormant and breaking buds were
classified into four developmental stages. Those stages were: ecodormant, initial
swelling, fully swollen, and broken buds. Isothermal experiments at 25°C were
done to evaluate metabolic heat rate, CO₂ evolution rate, and metabolic
efficiency. Also, buds were scanned from 1 to 60°C (7°C/hr) to estimate
activation energy and Q₁₀ values. Metabolic heat rates were 5, 17, 28, and 29
μW/mg dw, respectively, for the four bud developmental stages listed above. In
the same order, CO₂ evolution increased from 2 to 3, 6, and 7 /μW/mg dw. The
efficiency of metabolism, however, decreased during the initial swelling stage.
High apparent activation energy values for ecodormant and initial swelling buds
showed that metabolism at those stages is slow, mostly because it is energetically
expensive. As the buds developed, activation energy decreased, indicating a
more favorable condition from a thermodynamic standpoint. Q₁₀ values
demonstrated that grapevines are highly responsive to temperature. Water
content and respiration activity are useful indicators of metabolic activity.
