Regulation of pollen tube growth by cellular pH and ions.

Tip growth of the pollen tube is a model system for the study of cell polarity establishment in flowering plants. The tip growth of the pollen tube displays an oscillating pattern corresponding to cellular ion and pH dynamics. Therefore, cellular pH and ions play an important role in pollen growth and development. In this review, we summarized the current advances in understanding the function of cellular pH and ions in regulating pollen tube growth. We analyzed the physiological roles and underlying mechanisms of cellular pH and ions, including Ca2+, K+, and Cl-, in regulating pollen tube growth. We further examined the function of Ca2+ in regulating cytoskeletons, small G proteins, and cell wall development in relation to pollen tube growth. We also examined the regulatory roles of cellular pH in pollen tube growth as well as pH regulation of ion flow, cell wall development, auxin signaling, and cytoskeleton function in pollen. In addition, we assessed the regulation of pollen tube growth by proton pumps and the maintenance of pH homeostasis in the trans-Golgi network by ion transporters. The interplay of ion homeostasis and pH dynamics was also assessed. We discussed the unanswered questions regarding pollen tube growth that need to be addressed in the future.

Roles of TOR signaling in nutrient deprivation and abiotic stress.

In living organisms, nutrient, energy, and environmental stimuli sensing and signaling are considered as the most primordial regulatory networks governing growth and development. Target of Rapamycin (TOR) is a diversified Serine/Threonine protein kinase existing in all eukaryotes that regulates distinct salient growth and developmental signaling pathways. TOR signaling acts as a central hub in plants that allows a variety of nutrients, energy, hormones, and environmental stimuli to be integrated. TOR is activated by several nutrients and promotes energy-consuming processes such as cell division, protein translation, mRNA translation and ribosome biogenesis. We summarized the recent findings on the TOR function in regulating the dynamic networks of nutrients, including sugar, sulfur, nitrogen, carbon, phosphorus, potassium, and amino acids. TOR's role in abiotic stress was discussed, in which TOR orchestrating stress signaling, including heat, cold, salt, and osmotic stress, to regulate transcriptional and metabolic reprogramming, as well as growth and development. The interconnections between TOR and SnRK1 kinase were discussed in controlling nutrient deprivation and abiotic stress.

Small signaling molecules in plant response to cold stress.

Cold stress is one of the harsh environmental stresses that adversely affect plant growth and crop yields in the Qinghai-Tibet Plateau. However, plants have evolved mechanisms to overcome the impact of cold stress. Progress has been made in understanding how plants perceive and transduce low-temperature signals to tolerate cold stress. Small signaling molecules are crucial for cellular signal transduction by initiating the downstream signaling cascade that helps plants to respond to cold stress. These small signaling molecules include calcium, reactive oxygen species, nitric oxide, hydrogen sulfide, cyclic guanosine monophosphate, phosphatidic acid, and sphingolipids. The small signaling molecules are involved in many aspects of cellular and physiological functions, such as inducing gene expression and activating hormone signaling, resulting in upregulation of the antioxidant enzyme activities, osmoprotectant accumulation, malondialdehyde reduction, and photosynthesis improvement. We summarize our current understanding of the roles of the small signaling molecules in cold stress in plants, and highlight their crosstalk in cold signaling transduction. These discoveries help us understand how the plateau plants adapt to the severe alpine environment as well as to develop new crops tolerating cold stress in the Qinghai-Tibet Plateau.