Seed structure and germination in Cuscuta pedicellata with some notes on C. campestris

Dry seeds of Cuscuta pedicellata have a deeply pitted surface due to invaginated epidermal cell walls. After water uptake these walls bulge outwards and the seed surface becomes papillose. The seed coat consists of an epidermis, two palissade cell layers, and a multiple layer of parenchyma cells. The epidermis contains starch and mucilage, the parenchyma cells are compressed but some contain starch. The endosperm consists of starch–filled cells, but has a peripheral aleuron layer. The endosperm cell walls are gelatinous. The variable structure of the seed coat epidermis is believed to function in wind dispersal and rapid water uptake. Seed dormancy is common in the genus, but does apparently not occur in C. pedicellata.     

Decomposition of plant residues at low temperatures separates turnover of nitrogen and energy rich tissue components in time

Carbon and nitrogen loss patterns from stems and leaves from Elephant grass (Miscanthus × ogiformis Honda cv. Giganteus), and five commonly used cover crop species: Hairy vetch (Vicia villosa Roth), Italian ryegrass (Lolium multiflorum L.), Crimson clover (Trifolium incarnatum L.), Rye (Secale cereale L.), and Radish (Raphanus sativus L.) were examined at 3 and 9 °C. The stratified incubation system allowed `dry' recovery of the decomposing plant residues with minimal soil contamination and without loss of soluble substances. The recovered materials were characterized biochemically and by light and scanning electron microscopy. When the data was analysed across all treatments and sampling dates, there was no significant effect of temperature on N loss, whereas C loss was significantly affected (P<0.0001) by temperature. Decomposition at 3 °C led to wider C-to-N ratios in the plant residues. At 3 °C there was no net immobilization of N, whereas at 9 °C net immobilization was strong in the L. multiflorum and M. × ogiformis treatments. The biochemical and microscopic evidence supports that microbial growth and macro-polymer utilization was reduced at 3 °C. It was apparent that the dicot materials leaked substantially more carbon during the early phase of decomposition, whereas in the monocot materials and especially in the M. × ogiformis treatment the microbial growth and substrate utilization must have been contained within the decomposing tissues. Based on this evidence, we propose that the decomposition of intracellular low molecular substances and proteins can be viewed as a process separate from the decomposition of macro-polymers in cell walls. At higher temperatures these processes coincide and thus the distinctiveness is blurred, whereas at low temperatures they may occur more separated in time as well as space due to leaking.     

Accumulation of Metabolites during Seed Development in Trifolium repens L.

Metabolite deposition during seed development was examined histochemicallyin Trifolium repens by light- and fluorescence microscopy. Allendosperm haustorium at the chalazal pole of the embryo sacand wall protrusions in cell walls of the suspensor and theembryo sac suggest that transfer of metabolites from maternalto offspring tissue takes place primarily at these sites. Thisis further supported by prominent cutinization of the interpolarregion of the embryo sac wall, accumulation of starch in integumentaltissue at the embryo sac poles, and breakdown of interpolarendothelial cells. Decomposition of osteosclereid starch isfollowed by accumulation in the cellular endosperm and subsequentlyin the embryo parallel to endosperm degradation. The starchaccumulates gradually inward from the subepidermal cells ofthe embryo to the stele. Protein bodies are formed in the vacuolesalong the tonoplast, later to be cut off in vesicles releasedinto the cytoplasm. At maturity the embryo is packed with proteinand starch, but without lipid reserves. Phytin is observed inthe protein bodies. The mature embryo is surrounded by a proteinand starch containing aleurone layer which originates from theendosperm.Copyright 1994, 1999 Academic Press White clover, protein, starch, cuticle, embryo sac wall     

Phosphorus (P) acquisition of cereal cultivars in the field at three levels of P fertilization

Low phosphorus (P) availability in soils and diminishing P reserves emphasize the need to create plants that are more efficient P users. Knowledge of P efficient germplasm among the existing cereal varieties may serve as the basis for improving soil P use by selection and breeding. We had identified some cereal cultivars (winter wheat: Kosack and Kraka; winter barley: Hamu and Angora; spring barley: Canut, Alexis, Salka, Zita;) which differed (p<0.05) in P depletion from thin slices (0.2 mm) of the rhizosphere soil under controlled conditions. In the present study, the same cultivars were studied under field conditions at three levels of P supply (no-P, 10 and 20 kg P ha^-1) and the differences in P uptake as found in the previous work were confirmed. Under both conditions, the variation between the cultivars was greatest in soil without P fertilizers (no-P) for about 30 years. The variation in P uptake with most cultivars disappeared when 10 kg P ha^-1 was applied. Root development did not differ between the cultivars much, but there was wide, consistent variation in their root hairs, regardless of growth media (solution, soil column and field). Increase in soil P level reduced the length of root hairs. The variation in root hairs between the cultivars was largest in no-P soil. When 10 kg P ha^-1 was applied, the root hair lengths did not differ between the cultivars. Barley cultivars with longer root hairs depleted more P from the rhizosphere soil and also absorbed more P in the field. The relationship between root hairs and phosphorus uptake of the wheat cultivars was less clear. The wide variation in P uptake among the barley cultivars in the field and its relationship to the root hair development confirms that root hair length may be a suitable plant characteristic to use as criterion for selecting barley cultivars for P efficiency, especially in low-P soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Morphological and anatomical features of Cuscuta pedicellata and C. campestris

Observations on morphological and anatomical features of Cuscuta pedicellata and, to a lesser extent, C. campestris have been made at different stages of their life-cycles. The seedling is filiform with a bulbous radicular end which collapses early. The simple shoot apex is green and photosentitive. Initial "nutation" is followed by "creeping" over the substrate. Host plants less than about three weeks old seem not to be attacked by Cuscuta seedlings. When haustorial contact is established the shoot apex differentiates into buds and scale leaves. The chlorophyll disappears and stomata, which are lacking in the seedling, develop. The apical growth rate increases strongly by frequent cell division and - elongation. This is reflected anatomically by the formation of "cell families" in rows. Weakening and flowering of the host plants are followed by flowering of the parasite. Greening of stem segments of Cuscuta occurs during formation of haustoria and after death of the host. Stem anatomy is characterized by a tripartite cortex in which the middle layer consists of thin-walled angular cells. Characteristic are also the voluminuous intercellular spaces, the cortical and perivascular laticifers, and the central position of the small vascular bundles. Observations on self-parasitism were made. The epidermis of the haustorial cushion elongates and the cytoplasm is mainly positioned towards the host. Pseudo-intercellular spaces are formed between the epidermal cells. The haustorium connects the phloem of the two plants, but vascular elements of any kind have not been observed.     

Studies on the mucilaginous cells in the leaf ofSpartocytisus filipes W.B.

The structure and ultrastructure of epidermal cells with thick mucilaginous inner walls were investigated in leaves ofSpartocytisus filipes. Identification of the main constituents of the wall was attempted by means of histochemistry and polarized light and compared with the ultrastructure of the wall, which showed a mosaic structure alternating with electron dense bands.