The Essential Role of Calcium Ion in Pollen Germination and Pollen Tube Growth

Abstract

THE ELONGATION of the pollen tube in flowering plants is exceedingly rapid and its requirements, in general, seem quite unimpressive, i.e., water, oxygen and a suitable osmotic milieu. Despite extensive attempts to hasten this growth process with the conventional host of growth factors, few have met with convincing success. Boron, as borate, is the only factor previously shown to enhance growth markedly in a wide range of species. Its role is completely enigmatic. It is the purpose of this report to show that calcium ion plays a similarly prominent role in pollen germination and pollen-tube growth. The role of calcium, like that of boron, remains an intriguing enigma. A preliminary report of these findings has been made (Kwack and Brewbaker, 1961).MATERIALS AND METHODs-Several hundred flowering plant species were used in these tests. Most intensive studies were made with 2 selfincompatible species, Petunia infiata and Ornithogalum virens, which were brought to flower in controlled growth chambers. Ornithogalum virens (n = 3) was used in all studies; like many of its liliaceous relatives, it has large pollen grains, rapid pollen germination and growth, and clearcut responses to growth constituents.The basal medium for most studies included 10% sucrose and 100 ppm boric acid in deionized ABSTRACT BREWBAKER, JAMES L., and BEYOUNG H. KWACK. (U. Hawaii, Honolulu.) The essential role of calcium ion in pollen germination and pollen tube growth. Amer. Jour. Bot. 50 (9): 859-865. lIlus. 1963.-A pollen population effect occurs whenever pollen grains are grown in vitro. Small pollen populations germinate and grow poorly if at all, under conditions which support excellent growth of large pollen populations. The pollen population effect is overcome completely by a growth factor obtained in water extracts of many plant tissues. This factor is shown to be the calcium ion, and its action confirmed in 86 species representing 39 plant families. Other ions (K+, Mg"", N a") serve in supporting roles to the uptake or binding of calcium. The high requirement of calcium (300-5000 ppm, as Ca (N03),·4H20, for optimum growth) and low calcium content of most pollen may conspire to give calcium II governing role in the growth of pollen tubes both in vitro lind in situ. It is suspected that ramifications of this role extend to the self-incompatibilities of plants lind to the curious types of arrested tube growth distinguishing, for example, the orchids. A culture medium which proved its merit in II wide variety of pollen growth studies included, in distilled water, 10% sucrose, 100 ppm H 3B03, 300 ppm ell (NO,)2·4H20, 200 ppm MgS04·7H20 lind 100 ppm KNO,. distilled water; this is referred to as the 10: 100 solution. Pollen grains were sown in standing drops of 1/50 ml on cover slips. The cover slips were then placed on moist filter paper in Petri dishes, and normally left in room temperature during growth (up to 24 hr). Extensive studies were made of refinements of this technique (sterilization, humidity control, etc.), and of other techniqu...

Styrian oil pumpkin pollen germinability at higher irradiation doses: optimization of the in vitro germination protocol and irradiation procedure

“…In vitro pollen germination was extensively studied by Brewbaker and Kwack (1963) for a number of plant species, including genera of the family Cucurbitaceae (Cucumis, Lagenaria, and Momordica). Although semisolid modified BK medium was used to evaluate the effects of gamma irradiation on pollen germination in 2 species of Cucurbita (Kurtar, 2009), the author did not provide any information on the optimization of in vitro germination conditions.…”

Effects of Ca2+ on in vitro pollen germination of three Acacia species

“…This phenomenon has been confirmed in the research on a variety of plants (Tian and Yuan, 2000). It has been shown from the results of previous study that the culture medium of in vitro pollen germination needs a certain amount of Ca 2+ (Brewbaker and Kwack, 1963). In this study, with the treatment of Ca …”

Significance of stigma receptivity in intergeneric cross-pollination of Salix × Populus

“…Morphological traits of stigmas as markers of their receptivity have been assessed for some species, however, the only accurate method to prove SR is pollen germination test and seed-set registration [27][28][29][30][31]. Other methods of determining receptivity focus on indication of the activity of enzymes such as esterases, peroxidases, and acid phosphatases, on the stigma surface [32][33][34][35].…”

“…After 3 weeks of forcing, freshly released mature pollen grains were collected at 9:00 p.m. to evaluate pollen shape, ornamentation, aperture, and viability by staining with DAPI or 2% solution of tetrazolium chloride TTC [30]. At the same time, viability of poplar pollen was tested for germination efficiency in vitro and incubated under dark condition at 25°C on a modified BK liquid medium [31] (saccharose 5%, H 3 BO 3 100 mg L −1 , Ca(NO 3 ) 2 300 mg L −1 , pH 6.5). Pollen germination was analyzed quantitatively under light microscope for at least 100 grains taken from each sample.…”

“…After 24 h -1 DA, 36 h -2 DA, and 48 h -3 DA stigmas were removed from pistils, squashed in 0.05% aniline blue or DAPI, and examined using epifluorescence microscopy (Zeiss Axioscope, Jena, Germany). Pollen was considered as germinated when the pollen tube had a length that was greater than the diameter of the poplar pollen grain [30,31]. The percentage of pollen grains germinating was calculated on the stigmas of willow and poplar.…”