VASCULAR CAMBIAL SUCROSE METABOLISM AND GROWTH IN LOBLOLLY-PINE (PINUS-TAEDA L) IN RELATION TO TRANSPLANTING STRESS

Sucrose synthase (SS) was the dominant enzyme of sucrose metabolism in both stem and root vascular cambial zone tissues of nursery-grown lob lolly pine (Pinus taeda L.) seedlings. Acid invertase (AI) and neutral invertase (NI) activities were generally less than 10% of the SS acti vity in both tissues. In both cambial tissues, seasonal patterns of en zyme activity were observed for SS but not for AI or NI. The seasonal patterns of SS activity in stem and root cambia paralleled the periodi c growth of stems and roots. Stems had high SS activity and growth dur ing summer and early fall. Roots had substantial SS activity and growt h during summer and fall, but SS activity and growth were even higher in winter. When seedlings were transplanted, about eight months elapse d before stem and root cambia resumed rates of growth and sucrose meta bolism similar to those in control nontransplanted seedlings. Two mont hs after transplanting, root SS was at its lowest, whereas AI activity in transplants was 50% higher than in control nontransplanted seedlin gs. In stems, SS activity decreased in response to transplanting, wher eas AI and NI activities did not change appreciably. In loblolly pine tissues, SS was specific for uridylates, whereas the nucleotide tripho sphate-dependent phosphofructokinase (NTP-PFK) had similar activity wi th either UTP or ATP. Except in winter, the NTP-PFK was less active th an the pyrophosphate-dependent phosphofructokinase (PPi-PFK) during al l seasons. The PPi-dependent PFK activity in nontransplanted seedlings followed similar seasonal and spatial patterns to those of SS activit y. In actively growing tissues, such as stem cambial tissues in summer and root cambial tissues in winter, the measured total PFK to SS rati o ranged between 1.5/1 and 3/1. In contrast, in less actively growing tissues or transplanted seedlings, a greater decrease occurred in SS t han in PFK activity, hence the ratio rose to as high as 12/1. It was c oncluded that: (1) SS was the dominant enzyme for sucrose metabolism i n root and stem cambial tissues of loblolly pine seedlings; (2) both S S and PPi-PFK in the cambial tissues can be used as biochemical indica tors of growth sink strength in stems and roots; and (3) both enzymes can be used as indicators of seedling stress caused by events such as transplanting and winter freezing.