Abstract: The Type-Ⅰstomatal complex of citrus leaf forms at early developmental stage and
consists of 6–8 subsidiary cells and two big stomatal guard cells. In this report，programmed cell death
（PCD）of Type-Ⅰstomatal guard cells and its role in modification of surface structure during leaf
expansion were studied with modified temporary slides preparation method and conventional paraffin
section technique，which were conducted on spring leaves of different developmental stages in five citruscultivars，including‘Inaba Wase’（Citrus unshiu），‘Harumi’tangor[C. reticulata ×（C. reticulata × C.
sinensis）]，‘Cara Cara’navel orange（C. sinensis），‘HB’pummelo（C. grandis）and‘Meigui Cheng’
（C. sinensis）. Results showed that stomatal density of lower epidermis presented a unimodal distribution
during leaf development，with a peak at two-thirds expanded stage. Degeneration rates of Type-Ⅰstomatal
apparatus were low in spring leaves of‘Inaba Wase’，‘Harumi’tangor and‘HB’pummelo at late
developmental stage. However，Degeneration ranges of Type-Ⅰstomatal apparatus were very high in
spring leaves of ‘Cara Cara’navel orange and‘Meigui Cheng’，with almost all Type-Ⅰstomatal guard cells
degenerated at matured stage in both cultivars. With DAPI staining，nuclear pyknosis with chromatin
condensation，followed by formation of apoptotic bodies，was generally observed in degenerated Type-Ⅰ
stomatal guard cells，suggesting that cells underwent PCD. PCD of Type-Ⅰstomatal guard cells resulted in
closure or disappear of Type-Ⅰstomata through shrinkage of the guard cells. And as Type-Ⅰstomatal
guard cells underwent PCD，distribution of size of stomatal inner pores in‘Cara Cara’navel orange and
‘Meigui Cheng’both became similar to that of‘Inaba Wase’.

Key words: citrus, guard cell, stomatal density, programmed cell death