Changes in embryo drying rates, the alignment of lipid bodies along the plasma membrane, and dehydrin-like proteins during the acquisition of desiccation tolerance in maize seed

Abstract

Preserving maize (Zea mays L.) seed quality during mechanical drying is an important concern in the seed industry. In this study, preconditioning (slow drying prior to fast drying treatments) was used to investigate embryo-drying rates, the alignment of lipid bodies along the plasma membrane, and dehydrin-like protein profiles during the acquisition of desiccation tolerance in maize seed. Ears of hybrid maize [B73 x (H99 x H95)] were harvested in 1998, 1999, and 2000 at ca. 55,50,40 and 32% moisture content (mc) and subjected to preconditioning (PC) (ear drying at 35°C and 0.47 m/s airflow rate) for 0,12,24, 36, and 48h prior to fast drying (shelled seed, 35°C and 5.10 m/s airflow rate) treatments to decrease moisture to ca. 13%. The mc of intact seed harvested at >50% mc decreased ca. 20% points (pts) during the PC phase (0 to 48h) whereas the embryo mc decreased about 3% pts. With advances in maturity, embryo-drying rates increased while intact seed drying rates decreased. Under rapid drying conditions, on the other hand, embryo mc declined at very rapid rates down to ca. 40%. These rapid drying rates slightly decreased with increases in maturation, and, consequently, embryo dehydration seemed to occur in a more organized fashion. Similar effects, but to a lesser degree, were observed with increases in PC time prior to fast drying. Alignment of lipid bodies occurred first in the root cap, followed by outer and inner core cells. However, cell plasmolysis and aberrations in or perhaps coalescence of lipid bodies, were evident in seed harvested at mc >40% and subjected to fast drying without PC. These aberrations decreased in severity with PC and field maturation and appeared to be associated with partial or incomplete lipid body alignment prior to fast drying. In seed subjected to fast drying conditions, there is a slight but detectable increase in dehydrin-like proteins with increases in PC time prior to fast drying, particularly in seed harvested at 55