Pollen Tube and Root-Hair Tip Growth Is Disrupted in a Mutant of Arabidopsis thaliana

Abstract

l h e expansion of both root hairs and pollen tubes occurs by a process known as tip growth. In this report, an Arabidopsis thaliana mutant ( t i p l ) is described that displays defects in both root-hair and pollen-tube growth. l h e root hairs of the fipl mutant plants are shorter than those of the wild-type plants and branched at their base. l h e tipl pollen-tube growth defect was identified by the aberrant segregation ratio of phenotypically normal to mutant seeds in siliques from self-pollinated, heterozygous plants. Homozygous mutant seeds are not randomly distributed in the siliques, comprising only 14.4% of the total seeds, 5.3% of the seeds from the bottom half, and 2.2% of the seeds from the bottom quarter of the heterozygous siliques. Studies of pollen-tube growth in vivo showed that mutant pollen tubes grow more slowly than wild-type pollen through the transmitting tissue of wild-type flowers. Cosegregation studies indicate that the root-hair and pollen-tube defects are caused by the same genetic lesion. Based on these findings, the TlPl gene is likely to encode a product involved in a fundamental aspect of tip growth in plant cells.

The nutritional control of root development

“…Subsequent developmental stages include root hair initiation (when a bulge begins to form in the trichoblast cell wall), tip elongation and finally root hair maturation. The observations that root hair length and root hair density can be affected independently by nutrient stress are consistent with genetic evidence that initiation and growth of root hairs are under separate genetic control (Gilroy and Jones, 2000;Schiefelbein et al, 1993).…”

Root Hairs

“…The rhd1 mutants have huge swellings that take up most of the outer surface of the hair cell ( Figure 18). As tip1 and rhd1 are both loss-of-function mutants these results suggest that the RHD1 and TIP1 genes restrict swelling size, presumably by restricting the area of wall that is loosened (Parker et al, 2000;Ryan et al, 1998;Schiefelbein et al, 1993;Schiefelbein and Somerville, 1990). The tip1 rhd1 double mutants have similar swelling dimensions to rhd1 single mutants, suggesting that TIP1 cannot affect swelling size unless the RHD1 gene product is present (Parker et al, 2000).…”

TIP1 is required for both tip growth and non‐tip growth in Arabidopsis

“…ra & Ju$ rgens, 1995). Root-hairs are ideal because they exhibit polar tip-growth, and mutations affecting their development have been identified (Schiefelbein & Somerville 1990 ;Schiefelbein et al, 1993 ;Masucci & Schiefelbein, 1994 ;Grierson et al, 1997). Root-hairs are cylindrical extensions from specialized cells in the epidermis.…”

“…Analysis of the segregation ratio of the F # population revealed a segregation ratio of wildtype to mutant of 4n73 : 1, consistent with the mutation being monogenic, recessive with decreased transmission. Complementation tests were carried out with the rhd1, rhd2, rhd3, rhd4, rhd6 and tip1-1 mutations which also exhibit abnormal hair-cell morphogenesis (Schiefelbein & Somerville, 1990 ;Schiefelbein et al, 1993 ;Masucci & Schiefelbein, 1994). Crosses between E2 and tip1-1 produced mutant F "…”