CYTOCHEMICAL-LOCALIZATION OF RESERVES DURING SEED DEVELOPMENT IN ARABIDOPSIS-THALIANA UNDER SPACEFLIGHT CONDITIONS

Successful development of seeds under spaceflight conditions has been an elusive goal of numerous long-duration experiments with plants on o rbital spacecraft. Because carbohydrate metabolism undergoes changes w hen plants are grown in microgravity, developing seed storage reserves might be detrimentally affected during spaceflight. Seed development in Arabidopsis thaliana plants that flowered during 11 d in space on s huttle mission STS-68 has been investigated in this study. Plants were grown to the rosette stage (13 d) on a nutrient agar medium on the gr ound and loaded into the Plant Growth Unit flight hardware 18 h prior to lift-off. Plants were retrieved 3 h after landing and siliques were immediately removed from plants. Young seeds were fixed and processed for microscopic observation. Seeds in both the ground control and fli ght plants are similar in their morphology and size. The oldest seeds From these plants contain completely developed embryos and seed coals. These embryos developed radicle, hypocotyl, meristematic apical tissu e, and differentiated cotyledons. Protoderm, procambium, and primary g round tissue had differentiated. Reserves such as starch and protein w ere deposited in the embryos during tissue differentiation. The aleuro ne layer contains a large quantity of storage protein and starch grain s. A seed coat developed from integuments of the ovule with gradual ch ange in cell composition and cell material deposition. Carbohydrates w ere deposited in outer integument cells especially in the outside cell walls. Starch grains decreased in number per cell in the integument d uring seed coat development. All these characteristics during seed dev elopment represent normal features in the ground control plants and sh ow that the spaceflight environment does not prevent normal developmen t of seeds in Arabidopsis. (C) 1996 Annals of Botany Company.