Anneli Kauppi

Initiation, structure and sprouting of dormant basal buds in Betula pubescens

Summary The morphological basis for sprouting in Betula pubescens E hrh ., is studied with special reference to the initiation, structure and number of buds at the base of the tree and their development into sprouts. The material consists of seedlings of varying ages and stumps of mature trees. The dormant basal buds begin life as axillary buds at the seedling stage, positioned in accordance with the leaf arrangement. These primary basal buds are initiated in the axils of retarded leaves, and it is perhaps partly for this reason that they remain in a protracted state of dormancy. This dormancy is no more than a superficial feature, however, as, unlike the axillary buds higher up the stem, they are engaged in constant growth. They also differ structurally from ordinary axillary buds, possessing a growth point and a few scales after the first growing season, but no foliage leaf primordia, and gaining more scales as they age, normally one whorl per year. Similarly the vascular connection of a dormant basal bud grows year by year in accordance with the radial growth of the tree, thus ensuring that the bud does not become buried within the wood. The basal buds normally increase in number as the seedling grows, the primary buds branching to form clusters of secondary buds located in the axils of their scales. This branching requires a some degree of bursting of the buds. The resulting clusters are also found to vary in structure. Felling causes the majority of the dormant basal buds to burst, but only a certain number develop into sprouts. These sprouts differ morphologically from seedlings, especially in their pattern of ramification.

Sprouting ability and significance for coppicing of dormant buds on Betula pubescens Ehrh. Stumps

The numbers of basal dormant buds and resulting sprouts and their distribution on the stumps of the trees were studied in specimens of Betula pubescens Ehrh. of vegetative and seedling origin of different ages and growing on peatland or mineral soil. The results suggest that the number of buds at the base of the tree varies markedly from one tree to another. The old and young trees had quite similar numbers of buds, but those on mineral soil had less than those growing on peatland. The highest numbers of basal buds were found on sprout‐origin trees. Although about 90% of the basal buds were found below ground level, 1/3 of the sprouts originated from above the ground. This discrepancy can be explained by the formation of bud clusters, since the majority of the sprouts were derived from buds which occurred singly or in very small clusters. The total number of basal buds explains only part of the observed variation in sprouting potential. More important is the formation of bud clusters during the maturation...

The morphological background to imbibition in seeds ofPinus sylvestris L. of different provenances

An examination was made of the structure of the coats of Scots pine (Pinus sylvestris L.) seeds of different provenance and the contribution of this factor to differences in imbibition. The seed coat layers derived from the integument, the sarcotesta, sclerotesta and endotesta did little to restrict imbibition, even though the sclerotesta of the northern provenance seeds was composed of a double multicellular layer and the sarcotesta contained large numbers of pigmented, phenol-bearing cells. In addition to the micropyle, the sclerotesta was found to possess structural openings at the chalazal end and at the ridge joining the two halves of the seed, but being covered by the pigmented cells of the sarcotesta, these did not allow water to enter any more than did the micropyle itself. Imbibition was chiefly regulated by the lipophilic covers surrounding the endosperm, which are mainly of nucellar origin, especially by the megaspore membranes nearest to the endosperm, the outer and inner exine. The nucellar cap covering the micropylar end of the endosperm proved to be impermeable to water, and its edge extended between the exine layers, which further enhanced the importance of the endosperm covers as regulators of imbibition.

Seasonal Fluctuations in Chlorophyll Content in Birch Stems with Special Reference to Bark Thickness and Light Transmission, a Comparison between Sprouts and Seedlings

Summary A comparison is made of the structural properties of the stems of sprouts and seedlings of Betula pubescens and B. pendula with respect to cortical photosynthesis by studying the thickness and chlorophyll content of the chlorenchyma in parts of the stem of differing age at various times in the year, paying particular attention to the thickness and light transmission capacity of the phellem. The birch stems had a mean chlorophyll content of approx. 0.5–0.8 mg (gFW) -1 in the tissue lying immediately beneath the phellem all the year round. This total chlorophyll concentration remained virtually constant in the middle of winter, increased in early spring, and fell sharply upon emergence of the leaves. It then rose considerably again at the beginning of the growing season, especially in the younger annual shoots, falling once more in late summer and the early part of the winter. A distinct annual rhythm was also detected in the chlorophyll a/b ratio, which was similarly connected with the emergence and shedding of the leaves, the ratio being substantially higher during the leafless period of the year than in the summer (maximum in December and minimum in May). Both the chlorophyll a/b ratio and total chlorophyll fell markedly with age of the shoots, along with a thickening of the cork cell layers and a decline in its light transmission properties. The amount of chlorophyllous tissue increased with the age of the tree (1–20 years), however. Differences in the light transmission capacity of the phellem were observed between the plants of sprout and seed origin and to some extent between the species of birch, and these were reflected in the stem chlorophyll concentrations. The cork of the sprouts usually transmitted light better than that of the seedlings, this being more marked in Betula pubescens than in B. pendula. In all cases the best transmission capacity was found with respect to infra-red radiation of wavelength 725 mm, but large amounts of light at the photosynthetically active wavelength of 665 nm was also transmitted. The transmission properties altered with the thickening of the phellem and changes in its colour. The present pilot study reveals that young birch shoots would seem to possess a capacity for photosynthesis in their stem chlorenchyma which could be of ecological significance particularly in the leafless periods in early spring and late autumn. The differences between Betula pubescens and B. pendula and between the sprouts and seed origin shoots are nevertheless not of a magnitude that they could explain the more rapid early growth of the sprouts or the differences in sprouting capacity between the two species.

The significance of structure for imbibition in seeds of the Norway spruce, Picea abies (L.) Karst.

Since the observations of those regularly handling Norway spruce [Picea abies (L.) Karst.] seeds with regard to their imbibition frequently disagree with earlier opinions that this process is markedly inhibited by the seed coat, we decided to examine the morphological factors influencing imbibition in seeds of different colour and different provenances. The seed coat, consisting of the sarcotesta, sclerotesta and endotesta, was found to have little influence on the passage of water, despite the presence of sclereids full of wax lamellae. No differences in seed coat structure were observed between provenances or colours of seeds. The cells of the endotesta were lignified in the area of the micropyle, however, and stood out lip-like on the outer surface of the micropyle after imbibition. An opening in the sclerotesta filled with parenchyma cells was also seen at the chalazal end of the seed. Neither of these openings, which were covered by accumulations of wax, served as the main route for the passage of water, though the micropyle opened up slightly after only 24 h incubation, when the lignified cells bordering it swelled differently from the rest of the endotesta. The progress of water into the seed soon discontinued, however, as the tip of the nucellar cap, covered with wax and crystals, effectively plugged the micropyle. This opening of the micropyle may be the reason why the IDS method does not always succeed in separating viable from non-viable spruce seeds sufficiently well by their density. Imbibition was mostly regulated by the lipophilic layers surrounding the endosperm, which are mainly of nucellar origin, and particularly the megaspore membranes, the outer and inner exine. Imbibition was further hampered by the impermeable nucellar cap, which covered about 3/4 of the length of the endosperm and had merged with the outer exine at its edges. Deposits of wax were observed both between the exines and between the endotesta and the nucellar layers at the edges of the nucellar cap. Waxes may serve as a defence against diseases at the sites of water penetration, while simultaneously increasing the significance of the nucellar endosperm covers as regulators of imbibition.

Coppicing as a means for increasing hardwood biomass production

Abstract This report summarizes work done under the International Energy Agency Activity entitled “Developing the coppicing potential of selected hardwoods”. Altogether, 26 papers and publications have been prepared under this project, discussing a large number of coppicing mechanisms and factors of many important short-rotation hardwood tree species, the main emphasis being on birch, poplar, alder and willow. Coppicing research is reviewed briefly on the basis of two inquiries. There were 20 research projects and a total of 39 researchers dealing with coppicing in the various participating countries. A survey of coppicing problems indicates a need for scientific projects in ecophysiology, anatomy and stand dynamics.

Origin, Structure and Shoot-Formation Ability of Buds in Cutting-Origin Stools of Salix ‘Aquatica’

Summary The cultivation of trees and their use as an energy source have been investigated intensively during the last twenty years. Fast growing willows are the species to which most attention has been paid in Northern Europe in the context of short-rotation coppicing stands. Basic research into sprouting in these species is still quite insufficient, however, especially regarding the bursting dynamics of the buds and the shooting intensity of willows. The present work describes the structure and numbers of buds in cutting origin stools of Salix ‘Aquatica’ coppiced twice and four times. It was normal that two accessory, collateral buds developed at the base of the primary axillary bud all these then being covered by two solid, overlapping scales. The primary bud usually burst first, and after that the accessory buds could burst at any time, but sometimes only after a few years. Most of the new shoots grew on the sideshoots above ground level, although the shooting intensity of the buds was greatest on the mainstem. The buds located at ground level also produced shoots very well, but these were small in number. Coppicing markedly accelerated the growth of the accessory buds into shoots, the number of sideshoots trebling in two weeks. Since the shooting intensity of the willows increased markedly even after the fourth annual coppicing, Salix ‘Aquatica’ may be said to withstand many repeated coppicings, and thus appears to be suitable for short-rotation cultivation in this respect, too.

Calcium oxalate crystals in the mature seeds of Norway spruce, Picea abies (L.) Karst.

Abstract The morphology and location of crystals encountered in the mature seeds of Norway spruce, Picea abies (L.) Karst., were examined using light and field emission scanning electron microscopy (FESEM). Crystals of various forms and sizes were discovered in different regions and tissues of seeds, particularly in the testa and the nucellus. Both solitary crystals and druses were occasionally enveloped by protrusions of the megaspore membranes or the cuticle of the megagametophyte. Histological studies and acid solubility tests coupled with analysis using energy dispersive X-ray microanalysis and X-ray diffraction evinced the crystals as calcium oxalate, but were unable to identify different hydration forms. Calcium oxalate crystals were most abundant in the damaged and infected tissues, and in the structures that desiccate during the development of the seed. Based on these observations we concluded that the accumulation of calcium oxalate is a regular process belonging to maturation and defense mechanism in spruce seeds.

Pine embryogenesis: many licences to kill for a new life.

In plants, programmed cell death (PCD) is an important mechanism that controls normal growth and development as well as many defence responses. At present, research on PCD in different plant species is actively carried out due to the possibilities offered by modern methods in molecular biology and the increasing amount of genome data. The pine seed provides a favourable model for PCD because it represents an interesting inheritance of seed tissues as well as an anatomically well-described embryogenesis during which several tissues die via morphologically different PCD processes.

Structures contributing to the completion of conifer seed germination

Abstract The variety of interpretations of the origin and role of the tissues surrounding the emerging radicle of conifer seeds prompted us to study changes during germination. The structures contributing to the opening of the seed coat and protrusion of the radicle in pine and spruce seeds were examined using light microscopy and field emission scanning electron microscopy. The opening of the seed coat was mainly mechanical and primarily affected by the enlargement of the imbibed endotesta cells lining the micropylar canal. The hypertrophied nucellar apex, swelling remnants and mucous substances in the micropyle further enhanced the testa splitting which was reinforced by the straightening of the folded nucellar cap. The expansion of the imbibed megagametophyte and the embryo were conducive to the seed coat opening only at a later stage. This was followed almost immediately by the appearance of the root cap showing an early geotropic response typical for taproots and assuring an immediate anchoring of the emerged embryo to the ground. The translucent tissue composed of elongating cell rows preceded and surrounded the protruding radicle and derived mainly from two origins: the micropylar end of the megagametophyte and the root cap. Observations about the origin of the sheath clarify the reasons for previous interpretations about the putative role of the massive embryo root cap in testa splitting and germination. The protective and adhesive function of the sheath is concluded to be essential to the conifer embryos, which present the epigeal type of germination.