Abstract
Cassava (Manihot esculenta Crantz) plant resists water-deficit stress by shedding leaves leading to adaptive water-deficit condition. Transcriptomic, physiological, cellular, molecular, metabolic, and transgenic methods were used to study the mechanism of cassava abscission zone (AZ) cell separation under water-deficit stress. Microscopic observation indicated that AZ cell separation initiated at the later stages during water-deficit stress. Transcriptome profiling of AZ suggested that differential expression genes of AZ under stress mainly participate in reactive oxygen species (ROS) pathway. The key genes involved in hydrogen peroxide biosynthesis and metabolism showed significantly higher expression levels in AZ than non-separating tissues adjacent to the AZ under stress. Significantly higher levels of hydrogen peroxide correlated with hydrogen peroxide biosynthesis related genes and AZ cell separation was detected by microscopic observation, colorimetric detection and GC-MS analyses under stress. Co-overexpression of the ROS-scavenging proteins SOD and CAT1 in cassava decreased the levels of hydrogen peroxide in AZ under water-deficit stress. The cell separation of the pulvinus AZ also delayed in co-overexpression of the ROS-scavenging proteins SOD and CAT1 plants both in vitro and at the plant level. Together, the results indicated that ROS play an important regulatory role in the process of cassava leaf abscission under water-deficit stress.
Highlights
Fruitlet abscission with exogenous benzyladenine (BA) treatment
Spermidine oxidization into hydrogen peroxide through PAO can be induced by the salinity in the apoplast of tobacco transgenic plants overexpressing apoplastic polyamine oxidase, the accumulated hydrogen peroxide results in the induction of either tolerance responses or programmed call death (PCD) depend on the levels of intracellular PAO proteins[39]
Tisi et al, (2011) proved that over-expressed PAO or increased spermidine supply enhanced in vivo hydrogen peroxide production in plant tissues. hydrogen peroxide derived from polyamine catabolism behaves as a signal for secondary wall deposition and for induction of PCD40
Summary
Fruitlet abscission with exogenous benzyladenine (BA) treatment. The results indicated that fruitlet abscission, regulated by reactive oxygen species, sugar and phytohormones, signals cross-talk between fruitlet cortex and seed. An in vitro stress-induced leaf abscission system was established to identify the abscission signaling molecules In this system, 1-mm-thick pulvinus strips, encompassing the AZ, were separated within 4 days of abscission at the AZ through cell wall degradation in an auxin depletion- and ethylene-dependent manner[1]. 1-mm-thick pulvinus strips, encompassing the AZ, were separated within 4 days of abscission at the AZ through cell wall degradation in an auxin depletion- and ethylene-dependent manner[1] Using this system, Sakamoto et al, (2008) demonstrated that hydrogen peroxide is involved in the abscission process in Capsicum plants. Transgenic cassava plants, over-expressing cassava SOD/CAT1 ROS-scavenging proteins, decreased the levels of hydrogen peroxide and ethylene in AZ under water-deficit stress, retarded the cell separation of the pulvinus AZ under water-deficit stress both in vitro and at the plant level. A preliminary model is presented to illustrate the process of cassava leaf abscission under water-deficit stress
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