Microscopic structure of Scots pine (Pinus sylvestris (L.)) needles during ageing and autumnal senescence

Abstract

Needle ageing and senescence were studied in Scots pine (Pinus sylvestris) trees growing in natural conditions with minimal anthropogenic influence. The four existing needle generations were analyzed by light and transmission electron microscopy before and during autumnal yellowing of the oldest needle generation. The change from green to yellow occurred within less than 4 days in central Finland. The structure of the oldest needles remained largely intact as long as they were green. Increase in mitochondrion size and hypertrophy of the phloem parenchyma were the only changes, probably related to the approaching senescence. In the yellow needles, the structure of the mesophyll tissue varied from nearly intact with reduced chloroplasts and higher numbers of plastoglobuli, to totally disintegrated cells. In the disintegrated cells, peroxisomes were absent, and chloroplasts were smaller with a patchy appearance and degraded, eventually emptylooking stroma. Mitochondria were enlarged, but retained integrity until the last stages of deterioration, and lipids increased. At the light microscopic level, vacuolar volume in mesophyll cells and cavity formation in transfusion tissue increased. Ageing was characterized by increases in the vacuolar volume and cytoplasmic lipids, altered appearance of vacuolar tannin from homogenous 'sandy', to large spherical drops and finally to a large mass in the mesophyll, and by hypertrophy and tannin accumulation in the phloem parenchyma. Changes related to needle ageing, senescence and cell location in the mesophyll tissue were discussed relative to findings with stress by strong light, weather conditions and ozone.

Vegetative buds, needles and shoot growth of Norway spruce are affected by experimentally delayed soil thawing in the field

“…The activity was not affected by the treatments, however. The annual increase in phloem cells with needle age has been reported also earlier in Pinus sylvestris (L.) needles (Paramesvaran, 1971;Kivimäenpää and Sutinen, 2007) but not in xylem tissue as we observed here. The number of sclerenchyma cells or that of phloem rows was not affect by the treatments or the needle age.…”

Unbiased Estimation of Norway Spruce (Picea Abies L. Karst.) Chloroplast Structure: Heterogeneity Within Needle Mesophyll Under Different Irradiance and [Co2]

“…Thus, the first mesophyll layer was not always representative for every structural characteristic and every treatment. This is in agreement with the findings of Kivimäenpää and Sutinen (2007) who reported that mesophyll cells near the epidermis of four year old needles of Pinus sylvestris had smaller chloroplasts with lower area of starch grains than cells in the inner part of the needle. Furthermore, Senser et al (1975) noticed in Picea abies that the chloroplasts in cells near to the epidermis had higher amounts of starch than cells near the central cylinder, according to the gradient in light intensity.…”

Scots pine provenance affects the emission rate and chemical composition of volatile organic compounds of forest floor

“…Autumnal litterfall did not take place before the BVOC sampling from the forest floor in Suonenjoki in the study year. The oldest needle generation (fourth in the study region) senesces, i.e., rapidly turns yellow, at the end of August -beginning of September, and drops later in Suonenjoki region (Kivimäenpää and Sutinen 2007). However, some needles from the lower parts of the canopy can drop earlier during the growing season, which was observed in all provenances here.…”