Coping with spring frost-effects on polyamine metabolism of Scots pine seedlings

Abstract

(1) Polyamines (PA) are ubiquitous polycations known to be involved in several phases of plant development as well as in tolerance to abiotic stresses. Phenols are complex secondary metabolites produced via the phenylpropanoid pathway that contain, e.g., cell wall compounds and antioxidants. Phenols are known to enhance chilling tolerance of plants. PA and phenolic pathways are connected via conjugation. In boreal coniferous forests spring frost has been considered to have severe effects on the survival of tree seedlings. Such effects are likely to increase in the future. The present study focuses on the role of PA and phenylpropanoid syntheses in the coping strategies of Scots pine exposed to cold temperatures during the vulnerable early seedling phase in late spring and early summer. We found that spring frost affects the expression of genes regulating PA metabolism and phenylpropanoid synthesis differently in above and below ground parts of the seedlings, whereas PA or phenol contents in tissues were not affected. The results suggest that Scots pine seedlings may not have time to develop metabolite level responses during a short period of freezing stress and, therefore, the originally different PA levels, especially in roots, may influence the tolerance of Scots pine seedlings to spring frost.

Polyamine Metabolism in Scots Pine Embryogenic Cells under Potassium Deficiency

“…CAT expression decreased under potassium deficiency ( Figure 2 ), which agrees with the view that in Scots pine cells, CAT protects against H 2 O 2 accumulation and oxidative stress, especially during active metabolism [ 48 , 49 ]. Likewise, TAT-D, an evolutionary conserved apoptotic nuclease [ 50 ], and RBR, which inhibits cell cycle progression [ 51 ], showed decreasing gene expression under potassium deficiency ( Figure 2 and Supplementary Table S5 ).…”

“…To extend our view of PA metabolic responses in Scots pine during different kinds of stresses, we summarized the results of the present study with our previous findings of Scots pine PA metabolism under potassium deficiency [ 4 ], osmotic [ 63 , 64 ], drought [ 36 ] and cold [ 48 ] stresses ( Table 2 ). In proliferating embryogenic cells, only Spm/t-Spm content increased under polyethylene glycol (PEG)-induced osmotic stress [ 63 ].…”

“…Unlike in the roots of Scots pine seedlings under severe drought stress [ 36 ], CAT expression was not upregulated in Scots pine embryogenic cells under potassium deficiency, PEG-induced osmotic stress [ 63 ] or SE induction [ 64 ], indicating that H 2 O 2 was not overproduced in embryogenic cells. However, the seedlings exposed to freezing temperatures indicated that one of the first responses was the upregulation of DAO expression [ 48 ], which could be related to the production of H 2 O 2 and launching some signaling pathways in root cells. It was also remarkable that ACL5 , which is connected to zygotic embryogenesis and vascular development in Scots pine [ 27 ], was most consistently downregulated under the potassium, drought, and osmotic stresses, which indicated the obvious reduction of developmental processes ( Table 2 ).…”

Changing winter climate and snow conditions induce various transcriptional stress responses in Scots pine seedlings

“…A prolonged snow cover weakens plants by impeding metabolic processes and reduces the length of the growth period (Sakai and Larcher, 1987). On the other hand, high winter and spring temperatures will result in early snowmelt and misleadingly ameliorated environmental conditions which promote dehardening and growth onset thus extending the risk period of frost damage (Beck et al, 2004;Hänninen, 2006;Muilu-Mäkelä et al, 2017). Low oxygen soil conditions caused by compacted snow or ice encasement (Martz et al, 2016) may be detrimental to plants by reducing the efficiency of cellular ATP production and, furthermore, leading to the accumulation of toxic metabolites as a result of the anaerobic metabolism (Fukao and Bailey-Serres, 2004).…”