Alluni’s wife, Fatima, told journalists on Sunday that she had received a faxed copy of Najiya al-Kati’s death certificate which shows Taysir’s mother died on Tuesday.
"I have given [the certificate] to our attorney and I am going to appeal tomorrow in Madrid against my husband's imprisonment," she said.
The Qatar-based Arab Committee for the Defence of Journalists added its weight to calls for Alluni to be released.
"The ill-based intentions against Alluni are clearly proven by proceedings of his trial which ignored responses of Alluni's defense team," its statement read.
"The Committee believes that charges against Alluni are politically motivated in the first place and have nothing to do with his professional or personal conduct."
Alluni, a Spaniard of Syrian origin, is awaiting the verdict in his trial as one of 41 people charged by Spanish authorities with links to or membership of al-Qaida.
Some of the group are suspected of playing a role in the 9/11 attacks in the United States.
Fatima Alluni is to ask for the
release of Taysir Alluni
Alluni, first arrested in September 2003, had been allowed to stay under house arrest due to health problems.
But he was placed in detention in Granada on Friday because authorities considered he might try to flee after he asked to go to Syria for his mother's funeral, which was refused.
The Spanish court at the time rejected his request, arguing that the high-profile journalist did not present any documentation indicating that his mother had died.
Alluni is to appear before a Madrid judge on Monday when he is expected to be formally placed under judicial detention.
The Aljazeera journalist became famous by securing the first television interview with al-Qaida chief Usama bin Ladin after the 9/11 attacks in the US.
Alluni, whose trial finished in July, has been accused of delivering money to an al-Qaida leader in Afghanistan and if convicted could face nine years in prison.
He has denied any links to the organisation. The verdict in his trial is expected on 26 September.