Ethylene-Mediated Regulation of A2-Type CYCLINs Modulates Hyponastic Growth in Arabidopsis.

Upward leaf movement (hyponastic growth) is frequently observed in response to changing environmental conditions and can be induced by the phytohormone ethylene. Hyponasty results from differential growth (i.e. enhanced cell elongation at the proximal abaxial side of the petiole relative to the adaxial side). Here, we characterize Enhanced Hyponasty-d, an activation-tagged Arabidopsis (Arabidopsis thaliana) line with exaggerated hyponasty. This phenotype is associated with overexpression of the mitotic cyclin CYCLINA2;1 (CYCA2;1), which hints at a role for cell divisions in regulating hyponasty. Indeed, mathematical analysis suggested that the observed changes in abaxial cell elongation rates during ethylene treatment should result in a larger hyponastic amplitude than observed, unless a decrease in cell proliferation rate at the proximal abaxial side of the petiole relative to the adaxial side was implemented. Our model predicts that when this differential proliferation mechanism is disrupted by either ectopic overexpression or mutation of CYCA2;1, the hyponastic growth response becomes exaggerated. This is in accordance with experimental observations on CYCA2;1 overexpression lines and cyca2;1 knockouts. We therefore propose a bipartite mechanism controlling leaf movement: ethylene induces longitudinal cell expansion in the abaxial petiole epidermis to induce hyponasty and simultaneously affects its amplitude by controlling cell proliferation through CYCA2;1. Further corroborating the model, we found that ethylene treatment results in transcriptional down-regulation of A2-type CYCLINs and propose that this, and possibly other regulatory mechanisms affecting CYCA2;1, may contribute to this attenuation of hyponastic growth.

Ethylene-induced differential petiole growth in Arabidopsis thaliana involves local microtubule reorientation and cell expansion.

• Hyponastic growth is an upward petiole movement induced by plants in response to various external stimuli. It is caused by unequal growth rates between adaxial and abaxial sides of the petiole, which bring rosette leaves to a more vertical position. The volatile hormone ethylene is a key regulator inducing hyponasty in Arabidopsis thaliana. Here, we studied whether ethylene-mediated hyponasty occurs through local stimulation of cell expansion and whether this involves the reorientation of cortical microtubules (CMTs). • To study cell size differences between the two sides of a petiole in ethylene and control conditions, we analyzed epidermal imprints. We studied the involvement of CMT orientation in epidermal cells using the tubulin marker line as well as genetic and pharmacological means of CMT manipulation. • Our results demonstrate that ethylene induces cell expansion at the abaxial side of the- petiole and that this can account for the observed differential growth. At the abaxial side, ethylene induces CMT reorientation from longitudinal to transverse, whereas, at the adaxial side, it has an opposite effect. The inhibition of CMTs disturbed ethylene-induced hyponastic growth. • This work provides evidence that ethylene stimulates cell expansion in a tissue-specific manner and that it is associated with tissue-specific changes in the arrangement of CMTs along the petiole.

Oral 5-fluorouracil in squamous cell carcinoma of the skin in the aged.

Multiple or recurrent squamous cell skin carcinoma is a rare tumor in the aged. These patients are currently treated with 5-fluorouracil (5-FU) cream as a local chemotherapy; in cases in which the disease progresses, few treatments are available. Two reports deal with the treatment of progressive squamous cell skin carcinoma with systemic 5-FU, but in only eight patients age less than 70 years. We prospectively investigated oral 5-FU therapy in 14 consecutive patients (average age 76 1/2 years) with histologically proven squamous cell skin carcinoma. The disease was aggressive, multiple, or recurrent and had not been eradicated by surgery, radiation therapy, topical 5-FU cream, and non-5-FU chemotherapy. Oral 5-FU was administered as mannitol-coated 5-FU tablets at the daily dose of 175 mg/m2 for 3 weeks every 5 weeks. Toxicity, effectiveness, quality of life, and compliance to therapy were evaluated. Total cycles amounted to 55 (range: 2-6, mean: 4 for each patient) at an average dose intensity of 740 mg/m2/week for from 12 to 36 weeks. Only gastrointestinal toxicity World Health grade I occurred. Quality of life and compliance to therapy were 90%. Therapy induced measurable improvement in nine patients (64.3%): two partial remissions (14.3%), three minimal remissions (21.4%), and four arrests of disease (28.6%) with a median duration of 30+ months. The study ended because of a lack of patients. We can conclude that, if elderly patients require chemotherapy because of progressive multiple or advanced squamous cell skin carcinoma, appreciable results may be obtained with oral 5-FU as a single agent.