Activation of MAPK signaling pathway during nitrogen-deficiency responses in Ulva Prolifera

Background: Ulva prolifera is one of the main seaweeds (or macroalgae) species that causes “green tides”. This alga inhabits the estuarine areas that exhibit changes in nutrient contents, which include changes in nitrogen (N) levels, while the mechanisms through which these microalgae resist N deficiency remains unclear. Results: We amplified the full-length sequences and quantified expression of genes involved in the nitrogen metabolism process, the data indicated that nitrate reductase, nitrite reductase, and glutamine synthase increased after nitrogen deprivation in Ulva prolifera. Hence, although the ratio of cell-wall regeneration did not change, the apoptosis rates of protoplasts of Ulva prolifera increased after this deficiency. Furthermore, a decreased in N supplies triggered the activation of MAPK signaling, and SB239063, a p38 MAPKα/β inhibitor, enhanced the effects of N deficiency on the mortality of protoplasts and decreased the capacity for cell-wall regeneration. Conclusions: All the data provided evidence that MAPK signaling had functional roles in helping U. prolifera adapt to fluctuations in N availability within a short time. Hence, the application of biochemical reagents on cell-wall regeneration on the surface of protoplasts provided a new perspective in the genetic breeding of Ulva prolifera.

Dynamics of structural polysaccharides deposition on the plasma-membrane surface of plant protoplasts during cell wall regeneration

In this study, dynamic changes in structural polysaccharide deposition on the plasma membrane and cortical microtubules (CMTs) behavior were monitored in protoplasts isolated from white birch callus using confocal laser scanning microscopy and atomic force microscopy. We focused on the influence of an environmental stimulus on cell wall regeneration in protoplasts by employing an acidic culture medium containing a high concentration of Ca2+ (the stress condition). Under the non-stress condition, cellulose microfibrils and callose were initially synthesized, and thereafter deposited on the plasma membrane as “primary cell wall material”. Under the stress condition, callose micro-sized fibers were secreted without cell wall regeneration. Behavior of CMTs labeled with mammalian microtubule-associated protein 4 with green fluorescent protein in transgenic protoplasts was monitored by time-lapse video analysis. Under the non-stress condition, CMTs behavior showed a linear arrangement at a fixed position, whereas unfixed manner of CMTs behavior was observed under the stress condition. These findings indicate that excessive Ca2+ affects cellulose synthesis and CMTs dynamics in plant protoplasts. Current study first demonstrated dynamics of cell wall regeneration and CMTs in woody protoplast, which provides novel insight to aid in understanding early stages of primary cell wall formation in plants.