Impacts of bud set and lammas phenology on root:shoot biomass partitioning and carbon gain physiology in poplar

Key message

Timing of bud set and occurrence of lammas in trees can alter growth partitioning (i.e., root:shoot ratios), while only bud set effectively modifies carbon gain by increasing photosynthesis-related physiological traits.

Abstract

Bud set and lammas (second bud flushing) phenology may strongly influence growth, physiology, and biomass in trees. To test effects of these phenological events, 54 individuals from 16 genotypes of black cottonwood poplar (Populus trichocarpa) were grown in a potted trial under greenhouse conditions (with extended daylengths promoting growth), followed by open-air cultivation (with natural daylengths promoting bud set and/or lammas). Trees were monitored for phenology, repeatedly measured for photosynthesis-related traits, harvested for biomass, and assessed for growth partitioning (separating above- and belowground parts). We grouped trees by phenology for comparisons: (1) trees with early summer bud set, (2) trees with early summer bud set that underwent lammas, (3) trees with late summer bud set (August), and (4) trees with bud set occurring in autumn (September). We found that bud set timing positively affected growth partitioning where earlier bud set resulted in shorter trees with higher root:shoot biomass ratios (by increasing root mass). Lammas growth altered these ratios by significantly increasing shoot growth relative to belowground growth. Trees with bud set occurring in late summer also had higher root:shoot biomass ratios (by increasing root mass) compared to trees setting bud in autumn. Occurrence of bud set coincided with modified physiology of the existing canopy where photosynthesis-related traits were enhanced relative to trees still actively growing. These physiological changes were unaltered by occurrence of lammas. This suggests that bud set prompts a significant, coordinated mechanism of higher carbon gain physiology and belowground biomass accumulation in plants within a “post-bud set” phase.

     

Increased ornithine decarboxylase activity and polyamine biosynthesis are required for optimal cytolytic T lymphocyte induction

The objective of the present investigation was to evaluate the requirement for increased ornithine decarboxylase (ODC) activity and polyamine biosynthesis in the induction of cytolytic T lymphocytes (CTL). In this regard, we have utilized alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC. DFMO treatment completely abrogated Con A-induced NW T-cell ODC activity. Similarly, DFMO treatment reduced putrescine and spermidine biosynthesis 100 and 87% respectively by the end of a 48-hr incubation period. Polyamine depletion reduced the Con A-mediated polyclonal induction of CTL by 52 and 81% at 24 and 48 hr of culture, respectively. The effect of DFMO on CTL induction could be reversed by the addition of exogenous putrescine. These data indicate that the observed effects of DFMO on CTL induction were mediated through inhibition of polyamine biosynthesis. Therefore, increased ODC activity and polyamine biosynthesis are required for optimal CTL induction. Furthermore, polyamine depletion did not impair IL-2 production; however, IL-2-dependent proliferation was reduced. These data are the first to discriminate between the requirement for polyamines with regard to IL-2 responsiveness, rather than IL-2 production, during a primary T-cell mitogenic response.