Gian Gabriele Franchi

The tapetum: Its form, function, and possible phylogeny inEmbryophyta

It appears that the tapetum is universally present in land plants, even though it is sometimes difficult to recognize, because it serves mostly as a tissue for meiocyte/spore nutrition. In addition to this main function, the tapetum has other functions, namely the production of the locular fluid, the production and release of callase, the conveying of P.A.S. positive material towards the loculus, the formation of exine precursors, viscin threads and orbicules (= Ubisch bodies), the production of sporophytic proteins and enzymes, and of pollenkitt/tryphine. Not all these functions are present in all land plants:Embryophyta. Two main tapetal types are usually distinguished in theSpermatophyta: the secretory or parietal type and the amoeboid or periplasmodial type; in lower groups, however, other types may be recognized, with greater or lesser differences. A hypothetical phylogenesis of the tapetum is proposed on the basis of its morphological appearance and of the nutritional relations with meiocytes/spores. The evolutionary trends of the tapeta tend towards a more and more intimate and increasingly greater contact with the spores/pollen grains. Three evolutionary trends can be recognized: 1) an intrusion of the tapetal cells between the spores, 2) a loss of tapetal cell walls, and 3) increasing nutrition through direct contact in narrow anthers.

Types of carbohydrate reserves in pollen: localization, systematic distribution and ecophysiological significance

Summary Dehiscing pollen grains of 901 species belonging to 104 dicot families and 15 monocot families were scored for starch reserves. Starch grains showed different physico-chemical properties i.e. colour after iodine - potassium iodide staining and birefringence or otherwise under polarized light. Further tests performed in a limited number of species revealed other kinds of carbohydrate reserves in the cytoplasm but outside plastids. From these observations, it results that carbohydrate reserves may be stored in plastids only (amyloplasts), in the cytoplasm but not in plastids, or in both. These kinds of pollen reserves are only partly in line with systematics, as only certain families consistently show the same type of reserve. These and previous findings suggest that the presence of polysaccharides in the cytoplasm prevents rapid decrease in viability due to desiccation. In this sense, our findings are in line with ecophysiological adaptations such as the respective pollination syndrome.

Partially hydrated pollen: taxonomic distribution, ecological and evolutionary significance

Abstract. The problem of the water content of pollen is reconsidered, especially the distinction between “partially hydrated pollen” (PH pollen), pollen with a water content greater than 30%, and “partially dehydrated pollen” (PD pollen), which has a water content of less than 30%. Both types have been found even in systematically contiguous groups or the same genus. Partially hydrated pollen, encountered in at least 40 families of angiosperms, has the advantage of germinating quickly, normally in a few minutes to less than an hour. Dispersal of highly hydrated pollen also occurs in orchids but for a different reason, i.e. to enable packaging of massulae. The disadvantage of pollen dispersed with a high water content is that water is readily lost and the pollen may desiccate and die unless it has biochemical or anatomical devices to retain water or phenological strategies, such as flowering when temperatures are not too high and when relative humidity is high. Most pollen of Gymnosperms and Angiosperms studied has, however, been found partially dehydrated.

Humidity stress responses in pollen of anemophilous and entomophilous species

Abstract Pollen grains of 10 anemophilous and entomophilous species of angiosperms were kept at 4 relative humidities (RH) (15, 51, 79 and 98%) and their viability tested by fluorochromatic reaction after time lapses ranging from 6 to 144 h. Pollen viability in the anemophilous species decreased more rapidly than in the entomophilous ones with the exception of the dioecious palm Chamaerops humilis. The modes of anther and flower opening, times of anther exposure etc. were recorded: Cytological data are discussed and compared with these aspects of reproductive ecology.

Cytochemistry of mature angiosperm pollen

The problems involved in applying histochemical and cytochemical methods to mature angiosperm pollen for bright light and fluorescence microscopy are discussed. These methods can be used for general examination or to reveal particular structures or groups of substances. The main methods of testing pollen viability and germinability based on stains and semiquantitative methods are also reviewed. The main methods of staining and their applications are summarised.

Amylogenesis and Amylolysis During Pollen Grain Development

In pollen mother cells, the organelles dedifferentiate at the onset of meiosis (Bird et al., 1983). Plastids previously containing starch are completely starch-free at zygotene (Bird et al., 1983; Pacini and Franchi, 1983). Organelle dedifferentiation is accompanied by ribosome reorganization (Bird et al. 1983). After telophase, plastids may differentiate again in the amyloplasts, but their behavioural pattern varies according to the species. At pollen shedding some species have starch and others have not (Baker and Baker, 1979; Franchi and Pacini, 1988).

Ripe pollen structure and histochemistry of some gymnosperms

Some aspects of pollen cytology at dispersal were studied in 12 species of gymnosperms. The pollen grains differed in: 1. volume and cell number; 2. polarization of external structure and internal cell components; 3. wall thickness, especially of the intine, and the resulting percentage of cell volume with respect to total pollen grain volume; 4. stratification and chemical nature of the various intine layers; 5. nature and location of polysaccharide reserves; 6. morphological differences between the dry and hydrated states and phenomena related to hydration; 7. presence and site of orbicles. The various characters are compared and discussed in relation to the length of the reproductive cycle and the relations between the male gametophyte and its female counterpart.

Variability of nectar production and composition in Linaria vulgaris (L.) Mill. (Scrophulariaceae)

Abstract. We studied nectar characteristics during the long flowering period (late June to end of November) in two populations of Linaria vulgaris (L.) Mill. spontaneously growing in the Botanical Gardens of Siena University (Tuscany, central Italy). The two populations were close to each other but they differed in blooming period. Plants of population 1 sprouted in May and flowered from the end of June to the end of September. Population 2 sprouted at the end of August and flowered from September to the end of November. Differences in nectar production and composition were found between and within populations. Flowers of population 1 produced a very small amount of nectar (not collectable) that remained on the nectary surface. The quantity of nectar increased in late September, when each flower produced 2–3 μl of nectar that flowed into the spur. Total sugar concentration was 175.8 mg/ml in young flowers. Flowers of population 2 produced 5–8 μl of nectar with a total sugar concentration of 200.9 mg/ml in the young stage. In bagged senescent flowers nectar volume decreased in both populations and nectar sugar concentration decreased down to 11.6 mg/ml in population 2 and increased up to 289.6 mg/ml in population 1. For both populations, the decrease in nectar volume in bagged flowers may have been due to water loss by evaporation. In population 2, the decrease in sugar concentration may have been due to nectar reabsorption that was never observed in population 1. Nectar variability is discussed in relation to insect visits and seed set.

High Performance Thin Layer Chromatographic Quantitative Analysis of Picrocrocin and Crocetin, Active Principles of Saffron (Crocus sativusL.‐Iridaceae): A New Method

A new high performance thin layer chromatographic method has been developed for the quantitative analysis of the active principles (picrocrocin and crocetin) of saffron (Crocus sativusL.). The method is easily applied, shows good reproducibility and is rapid and sensitive. The technique overcomes the problems usually found with other analytical approaches to saffron determination which generally are not repeatable and deal with identification of adulterations more than with the analysis of constituents.

Pollen grain viability in Parietaria judaica L. during the long blooming period and correlation with meteorological conditions and allergic diseases

Abstract Pollen grain viability and starch presence in pollen were followed during the long blooming period (May-November) of Parietaria judaica, the most widespread pellitory in Italy, responsible for many cases of allergic diseases. Observations were carried out near Siena (Tuscany), in the years 1978 and 1979. Viability is high in late spring and early autumn, and pollen grains are starchy. The presence of starchless grains is always related to low viability: a production of pollen with a low viability occurs at the beginning and end of blooming, and also in summer, during drought periods. Pollen grain viability varies widely during the blooming period, and its variations are correlated to meteorological conditions, mainly rainfall and temperature. Allergic diseases due to pellitory, however, are mainly reported between April and July, and on the other hand a small amount of patients states that they suffer all the year round. The discrepancies between the periods of viable pollen production and of dec...