Immature Pollen Grains Research Articles

Starch-synthesizing Enzymes in the Endosperm and Pollen of Maize

Two mutations, amylose-extender and waxy, which affect the proportion of amylose and amylopectin of starch synthesized in the endosperm of maize (Zea mays L.) seeds, are also expressed in the pollen. However, most mutations that affect starch synthesis in the maize endosperm are not expressed in the pollen. In an attempt to understand the nonconcordance between the endosperm and pollen, extracts of mature pollen grains were assayed for a number of the enzymes possibly implicated in starch synthesis in the endosperm. Sucrose synthetase (sucrose-UDP glucosyl transferase, EC 2.4.1.13) activity was not detectable in either mature or immature pollen grains of nonmutant maize, but both bound and soluble invertase (EC 3.2.1.26) exhibited much greater specific activity (per milligram protein) in pollen extracts than in 22-day-old endosperm extracts. Phosphorylase (EC 2.4.1.1) activity was also higher in pollen than in endosperm extracts. ADP-Glucose pyrophosphorylase (EC 2.7.7.27) activity was much lower in pollen than endosperm extracts, but mutations that drastically reduced ADP-glucose pyrophosphorylase activity in the endosperm (brittle-2 and shrunken-2) did not markedly affect enzymic activity in the pollen. Specific activities of other enzymes implicated in starch synthesis were similar in endosperm and pollen extracts.

Studies on the Haploid Formation from Immature Pollen Grain. : I. Relation between Pollen Stage and the Plantlet Formation and the Process of Embryoid Formation in Nicotiana tabacum.

Studies on the Haploid Formation from Immature Pollen Grain. : I. Relation between Pollen Stage and the Plantlet Formation and the Process of Embryoid Formation in Nicotiana tabacum.

Abnormal flower formation of tobacco plants regenerated from callus cultures

The plantlets regenerated from tobacco calluses, subcultured for prolonged periods, were weak and generally could not be cultivated into mature flowering specimens. However, some of them flowered and various kinds of abnormal flowers as well as leaves were observed in all the tobacco plants bearing flowers. They were sterile at had abnormal immature pollen grains. Some of them occasionally germinated in the anther. Abnormalities were also found in the nucleus of immmature pollen grains. Such drastic floral abnormalities were not found in tobacco plants derived from seeds and callus cultures subcultured for a relatively short period under the same conditions of cultivation.

Haploid Plantlets and Callus from Immature Pollen Grains of Nicotiana and Lycopersicon

Haploid Plantlets and Callus from Immature Pollen Grains of Nicotiana and Lycopersicon

Chromosome numbers of Cruciferae

Along with general taxonomie research on the Cruciferae of the Western Hemisphere and more intensive revisionary studies of particular genera, a continuous program of chromosome counting and breeding system testing has been underway for some years. In many cases, seeds have been obtained from wild sources and plants were grown in the greenhouse to provide either root-tips or flowering buds for chromosome counting. Otherwise, fixations of bud material have been made in the field. The distinction between greenhouse collections and field collections is made where the data are presented. In all instances, voucher specimens were prepared and deposited in the Gray Herbarium. The most significant immediate problem in which chromosome number information is helping to establish a measure of understanding concerns certain taxonomically complex species groups of Arabis. The initial breakthrough came from the work of Bocher ( 1951 ) in which he established the presence of apomixis in the genus. In subsequent studies (Bocher 1954, 1969), evidence for widespread apomixis in Arabis was increased and the frequent association of asymmetrical chromosome numbers with apomixis was established. Facultative apomixis appears to be the rule. Previous studies by one of us (Rollins 1941, 1966) support the general assumption that several agamic complexes exist in the genus. The additional chromosome counts presented below further add to the overall evidence for this assumption. In the following lists, the somatic counts from root-tips, or occasionally from some other somatic cell, are given as 2n, and those from pollen mother cells or immature pollen grains (microsporocytes) as n.