Organ abscission is a programmed cell separation process that results in the detachment of an entire organ from a plant. Our goal is to understand the signaling pathway that regulates this physiological process. The receptor-like protein kinase, HAESA (HAE), and its paralog, HAESA-like 2 (HSL2), are both expressed in the floral abscission zones in Arabidopsis thaliana. Loss-of-function analyses of either gene do not show any phenotypical change, but the hae hsl2 double mutant shows an abscission-defect phenotype. Examination of the abscission zone by light and scanning electron microscopy showed that the abscission zone in the hae hsl2 appears structurally normal. The force required to remove the petals in wild type and hae hsl2 flowers was measured using a petal breakstrength meter. The force required to remove petals from the hae hsl2flowers at all stages of development was similar to that of wild type flowers that have not yet begun to abscise their petals. Taken together, these data support the role of HAE and HSL2 in the activation of cell separation, rather than differentiation of the abscission zone. Ethylene is also known to promote abscission; therefore we tested the ethylene-induced triple response and the effect of exogenous treatment on floral organ in the hae hsl2, revealing that HAE and HSL2 act independently of ethylene. This implies that the HAE is critical for floral abscission in concert with the action of HSL2.

Nitrogen (N) fertilization is essential for alleviating nutrient deficiencies of the world’s population by increasing rice production, one of the most important food crops of our time. Here we established an in vivo hydroponics rice seedling culture system to investigate the physio-biochemical and molecular responses of various rice genotypes to low nitrogen application. Yoshida’s nutrient solution (YS) was used to grow rice seedlings, and at three-week-old the seedlings manifested highly stable and reproducible symptoms, such as reduced shoot growth and length. Out of 12 genetically selected or tested genotypes, almost all (11 genotypes) showed varied degrees of growth reduction response to applied nitrogen (4 and 40 ppm N for treatment and control, respectively), but SR19663-B-B-34-3-3-3-1 showed similar growth as the control though its leaf width was smaller than the control. The leaves of a 11 representative low nitrogen-responsive genotype as BG90-2 were sampled for revealing the protein profiles between low and normal (control) nitrogen application by using two-dimensional gel electrophoresis (2-DGE) followed by staining of separated proteins with silver. Fifty differentially expressed silver stained protein spots were excised from 2-D gels and 41 proteins identified using high-throughput mass spectrometry (MS) using matrix-assisted laser desorption/ionization-time of flight-MS and nano electrospray ionization liquid chromatography tandem MS. These proteins could be assigned as major (energy metabolism, photosynthesis and oxidative stress) and minor functional categories, revealing many novel low N-responsive proteins, including those having energy/photosynthesis, and defense/stress, and iron homeostasis-related functions.