Evidence that Tuber Respiration is the Pacemaker of Physiological Aging in Seed Potatoes (Solanum tuberosum L.)

Storage temperatures greater than 4 A degrees C (that is, heat-unit accumulation) increase respiration and accelerate physiological aging of seed tubers. The degree of apical dominance is a good indicator of physiological age (PAGE). As seed age advances, apical dominance decreases, resulting in more stems, greater tuber set, and shifts in tuber size distribution. Herein we provide evidence that tuber respiration rate may constitute the pacemaker of aging. Tubers exposed to a brief high-temperature age-priming treatment initially in storage, followed by holding at 4 A degrees C for the remainder of a 190-200-day storage period, maintained a higher basal metabolic (respiration) rate throughout storage compared with tubers stored the entire season at 4 A degrees C. Tubers thus remembered the age-priming treatment as reflected by their elevated respiration rate. Moreover, reducing the respiration rate of age-primed seed by subsequently storing it at 3.5 % O-2 (4 A degrees C) until planting significantly attenuated the effects of the aging treatment on apical dominance, tuber set, and size distribution. The effect of the age-priming treatment on the magnitude of the respiratory response was the same whether given at the beginning or toward the end of storage. However, moving the age-priming treatment progressively later in the storage season effectively decreased its impact on plant growth and development. These results underscore the importance of time in the aging process. Exposure of seed to a high-temperature age-priming treatment at the beginning or end of storage elevated respiration (the pacemaker) to the same extent; however, the timing of these treatments resulted in vastly different physiological ages. The longer the respiration rate of tubers remains at an elevated level, the greater their PAGE at planting. Thus, an accurate but impractical measure of PAGE may be the respiratory output from vine kill to subsequent planting. Respiration appears to be the pacemaker of PAGE and production, and storage conditions that affect respiration may set the clock speed that will ultimately determine the PAGE at planting.