Bong Soo Park

In the agricultural industry, the post-harvest leafy vegetable quality and shelf life significantly influence market value and consumer acceptability. This study examined the effects of different storage temperatures on leaf senescence, nitrogen assimilation, and remobilization in Pak Choi (Brassica rapa subsp. chinensis). Mature Pak Choi plants were harvested and stored at two different temperatures, 4 °C and 25 °C. Senescence was tracked via chlorophyll content and leaf yellowing. Concurrently, alterations in the total nitrogen, nitrate, and protein content were quantified on days 0, 3, 6, and 9 in old, mid, and young leaves of Pak Choi plants. As expected, 4 °C alleviated chlorophyll degradation and delayed senescence of Pak Choi compared to 25 °C. Total nitrogen and protein contents were inversely correlated, while the nitrate content remained nearly constant across leaf groups at 25 °C. Additionally, the transcript levels of genes involved in nitrogen assimilation and remobilization revealed key candidate genes that were differentially expressed between 4 °C and 25 °C, which might be targeted to extend the shelf life of the leafy vegetables. Thus, this study provides pivotal insights into the molecular and physiological responses of Pak Choi to post-harvest storage conditions.

Summary Phosphate (Pi) availability is a major factor limiting plant growth and development. The key transcription factor controlling Pi‐starvation response (PSR) is PHOSPHATE STARVATION RESPONSE 1 (PHR1) whose transcript levels do not change with changes in Pi levels. However, how PHR1 stability is regulated at the post‐translational level is relatively unexplored in Arabidopsis thaliana . Inositol polyphosphates (InsPn) are important signal molecules that promote the association of stand‐alone SPX domain proteins with PHR1 to regulate PSR. Here, we show that NITROGEN LIMITATION ADAPTATION (NLA) E3 ligase can associate with PHR1 through its conserved SPX domain and polyubiquitinate PHR1 in vitro . The association with PHR1 and its ubiquitination is enhanced by InsP6 but not by InsP5. Analysis of InsPn‐related mutants and an overexpression plant shows PHR1 levels are more stable in itpk4‐1 and vih2‐4/VIH1 amiRNA but less stable in ITPK4 overexpression plants. Under Pi‐deficient conditions, nla seedlings contain high PHR1 levels, display long root hair and accumulate anthocyanin in shoots phenocopying PHR1 overexpression plants. By contrast, NLA overexpression plants phenocopy phr1 whose phenotypes are opposite to those of nla . Our results suggest NLA functions as a negative regulator of Pi response by modulating PHR1 stability and the NLA/PHR1 association depends on InsPn levels.